Display Apparatus with Narrow Gap Electrostatic Actuators

ABSTRACT

This disclosure provides systems, methods and apparatus for incorporating tip-gap adjustment features (TGAF) in actuators of shutter assemblies. The TGAF are incorporated into a drive beam of the actuator during the formation of the shutter assembly over a mold. The TGAF are configured such that they develop a mechanical stress or stress gradient. When the shutter assembly is released from the mold, the stress or stress gradient in the TGAF bend the drive beam such that a tip-gap between the drive beam and a load beam of the actuator is reduced. The reduced tip-gap, in turn, reduces an actuation voltage needed to actuate the shutter assembly.

TECHNICAL FIELD

This disclosure relates to the field of imaging displays, and inparticular, to imaging displays employing electrostatic display elementsactuators.

DESCRIPTION OF THE RELATED TECHNOLOGY

Certain electromechanical systems (EMS) electrostatic actuators includeopposing beams supported over a substrate. A voltage needed to actuatesuch actuators is dependent in part on the minimum distance between thebeams. For example, the voltage needed to actuate the actuator decreaseswith the decrease in the minimum distance between the opposing beams. Insome implementations of such actuators, the voltage needed to actuatethe actuators is reduced as a result of inherent stresses building up inthe beam materials during their deposition, resulting in the tip of atleast one of the beams naturally and spontaneously bending towards theother beam, reducing the minimum distance between them.

Some manufacturing processes, however, do not result in the beamsbuilding up sufficient internal stress to yield this bending. As aresult, additional voltage may be needed to actuate such actuators,resulting in a more power-hungry and slower display.

SUMMARY

The systems, methods and devices of the disclosure each have severalinnovative aspects, no single one of which is solely responsible for thedesirable attributes disclosed herein.

One innovative aspect of the subject matter described in this disclosurecan be implemented in an apparatus having a substrate and anelectromechanical systems (EMS) electrostatic actuator coupled to thesubstrate. The electrostatic actuator can include a load beam electrodecoupled to a light modulator. The electrostatic actuator can alsoinclude a drive beam electrode having a first portion positionedadjacent to the load beam, a second portion positioned behind the firstportion with respect to the load beam, and an end portion connecting thefirst portion to the second portion, where the thickness of the secondportion varies along its length.

In some implementations, the second portion of the drive beam electrodeincludes a first generally U-shaped segment, where the thickness of thedrive beam electrode along the first generally U-shaped segment isdifferent than the thickness of the beam adjacent to the first generallyU-shaped segment. In some of these implementations, the second portionof the drive beam electrode includes a second generally U-shaped segmentand where the thickness of the drive beam electrode along the first andthe second generally U-shaped segments is different than the thicknessof the remainder of the second portion. In some implementations, thefirst U-shaped segment is adjacent to the second U-shaped segment.

In some implementations, the first portion of the drive beam electrodeincludes a third generally U-shaped segment, smaller than the firstU-shaped segment of the second portion. In some implementations, asegment of the second portion of the drive beam electrode has an anglewith respect to the substrate that is shallower than an angle formed bya remainder of the second portion of the drive beam electrode withrespect to the substrate. In some implementations, the segment of thesecond portion of the drive beam electrode having the shallower anglewith respect to the substrate is thinner than the remainder of thesecond portion of the substrate. In some implementations, the firstportion, the end portion, and the second portion of the drive beam forma loop.

In some implementations, the apparatus further includes a display, aprocessor that is configured to communicate with the display and toprocess image data, and a memory device that is configured tocommunicate with the processor. In some implementations, the apparatuscan further include a driver circuit configured to send at least onesignal to the display, and a controller configured to send at least aportion of the image data to the driver circuit. In someimplementations, the apparatus can further include an image sourcemodule configured to send the image data to the processor, where theimage source module includes at least one of a receiver, transceiver,and transmitter. In some implementations, the apparatus further includesan input device configured to receive input data and to communicate theinput data to the processor.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented in a display element having a substrateand an electromechanical systems (EMS) electrostatic actuator coupled tothe substrate. The electrostatic actuator includes a load beam electrodecoupled to a light modulator, and a drive beam electrode coupled to thesubstrate. The drive beam electrode includes a first portion positionedadjacent to the load beam electrode, a second portion positioned behindthe first portion with respect to the load beam electrode, an endportion connecting the first portion to the second portion. The beamelectrode also includes a shelf structure separate from an anchorsupporting the drive beam over the substrate, having a first planarsurface that is substantially parallel to the substrate and coupled tothe second portion of the drive beam.

In some implementations, the first planar surface is positioned on aside of the second portion of the drive beam that is substantiallynormal to the substrate. In some other implementations, the first planarsurface in positioned on an edge of the second portion of the drive beamthat faces away from the substrate. In some implementations, the shelfstructure includes a second planar surface that is substantiallyparallel to the substrate and coupled to the second portion of the drivebeam. In some implementations, the first planar surface and the secondplanar surface are positioned on opposite ends of a side of the secondportion that is substantially normal in relation to the substrate. Insome implementations, the shelf structure is physically separated fromthe first portion of the drive beam. In some implementations, the firstportion, the end portion, and the second portion of the drive beam forma loop.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented in a method including forming a mold overa substrate, forming a light modulator over a surface of the mold,forming a load beam coupled to the light modulator on a first sidewallof the mold, forming a first portion of a drive beam on a secondsidewall of the mold facing the first sidewall, and forming a secondportion of the drive beam on a third sidewall facing away from the firstsidewall, such that a thickness of the second portion varies along alength of the second portion.

In some implementations, the third sidewall includes a U-shaped portion,and forming the second portion further includes forming a generallyU-shaped segment in the second portion along the U-shaped portion of thethird sidewall such that a thickness of the second portion along theU-shaped segment is different from a thickness of the second portionadjacent to the generally U-shaped segment.

In some implementations, forming the mold further includes forming aportion of the third sidewall at an angle with respect to the substrate,the angle being shallower than that formed by the second sidewall. Insome such implementations, a segment of the second portion formed overthe portion of the third sidewall having the shallower angle is thinnerthan the remainder of the second portion.

Details of one or more implementations of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below. Although the examples provided in this summary areprimarily described in terms of MEMS-based displays, the conceptsprovided herein may apply to other types of displays, such as liquidcrystal displays (LCDs), organic light emitting diode (OLED) displays,electrophoretic displays, and field emission displays, as well as toother non-display MEMS devices, such as MEMS microphones, sensors, andoptical switches. Other features, aspects, and advantages will becomeapparent from the description, the drawings, and the claims. Note thatthe relative dimensions of the following figures may not be drawn toscale.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows an example schematic diagram of a direct-view MEMS-baseddisplay apparatus.

FIG. 1B shows an example block diagram of a host device.

FIG. 2 shows an example perspective view of an illustrativeshutter-based light modulator.

FIG. 3A shows an example schematic diagram of a control matrix.

FIG. 3B shows an example perspective view of an array of shutter-basedlight modulators connected to the control matrix of FIG. 3A.

FIG. 4A and FIG. 4B show example views of a dual actuator shutterassembly.

FIG. 5 shows an example cross sectional view of a display apparatusincorporating shutter-based light modulators.

FIGS. 6A-6E show cross sectional views of stages of construction of anexample composite shutter assembly.

FIGS. 7A-7D show isomeric views of stages of construction of an exampleshutter assembly with narrow sidewall beams.

FIGS. 8A-8C show various views of an example shutter assembly having afirst tip-gap adjustment feature.

FIG. 8D shows a top view of another example shutter assembly includingthe first tip gap adjustment feature.

FIGS. 9A-9H show various views of an example shutter assembly having asecond tip-gap adjustment feature.

FIGS. 10A-10C show various views of an example shutter assembly having athird tip-gap adjustment feature.

FIG. 11 shows a flow diagram of an example process for forming a shutterassembly with tip-gap adjustment feature.

FIGS. 12A and 12B show example system block diagrams illustrating adisplay device that includes a set of display elements.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

The following description is directed to certain implementations for thepurposes of describing the innovative aspects of this disclosure.However, a person having ordinary skill in the art will readilyrecognize that the teachings herein can be applied in a multitude ofdifferent ways. The described implementations may be implemented in anydevice, apparatus, or system that can be configured to display an image,whether in motion (such as video) or stationary (such as still images),and whether textual, graphical or pictorial. More particularly, it iscontemplated that the described implementations may be included in orassociated with a variety of electronic devices such as, but not limitedto: mobile telephones, multimedia Internet enabled cellular telephones,mobile television receivers, wireless devices, smartphones, Bluetooth®devices, personal data assistants (PDAs), wireless electronic mailreceivers, hand-held or portable computers, netbooks, notebooks,smartbooks, tablets, printers, copiers, scanners, facsimile devices,global positioning system (GPS) receivers/navigators, cameras, digitalmedia players (such as MP3 players), camcorders, game consoles, wristwatches, clocks, calculators, television monitors, flat panel displays,electronic reading devices (such as e-readers), computer monitors, autodisplays (including odometer and speedometer displays, etc.), cockpitcontrols and/or displays, camera view displays (such as the display of arear view camera in a vehicle), electronic photographs, electronicbillboards or signs, projectors, architectural structures, microwaves,refrigerators, stereo systems, cassette recorders or players, DVDplayers, CD players, VCRs, radios, portable memory chips, washers,dryers, washer/dryers, parking meters, packaging (such as inelectromechanical systems (EMS) applications includingmicroelectromechanical systems (MEMS) applications, as well as non-EMSapplications), aesthetic structures (such as display of images on apiece of jewelry or clothing) and a variety of EMS devices. Theteachings herein also can be used in non-display applications such as,but not limited to, electronic switching devices, radio frequencyfilters, sensors, accelerometers, gyroscopes, motion-sensing devices,magnetometers, inertial components for consumer electronics, parts ofconsumer electronics products, varactors, liquid crystal devices,electrophoretic devices, drive schemes, manufacturing processes andelectronic test equipment. Thus, the teachings are not intended to belimited to the implementations depicted solely in the Figures, butinstead have wide applicability as will be readily apparent to onehaving ordinary skill in the art.

The minimum separation distance between two opposing beam electrodes ofan electromechanical systems (EMS) electrostatic actuator can be reducedby introducing mechanical stress on one of the beams, causing it to bendtowards its opposing beam. In some implementations, one of the beamelectrodes is formed in the shape of an elongated loop. That is, a firstportion extends away from an anchor, and after a distance, curves backsuch that a second portion extends back towards and couples to theanchor. By introducing a stress or stress gradient on the second portion(i.e., the portion further from the opposing beam), the beam can be madeto bend towards the opposing beam.

In some implementations, this stress or stress gradient can beintroduced by forming the beam such that a thickness of the secondportion varies along its length. In some implementations, the variationof the thickness of the second portion of the beam is achieved byforming the second portion on sidewalls of a mold built on a substrate.Some sidewalls of the mold are configured to have an angle with thesubstrate that is shallower than the angle formed by the remainingsidewalls of the mold. This results in a part of the second portion thatis formed on these shallow angled sidewalls to be thinner than the restof the second portion. Due to this variation in the thickness, thesecond portion can develop a certain amount of stress or stressgradient. As a result, when the beam is released from the mold, thisstress or stress gradient causes the beam to bend towards the opposingbeam.

In some other implementations, the second portion of the beam includesone or more generally U-shaped beam regions. The beam material alongthese generally U-shaped beam regions is thinner than the beam materialadjacent to these U-shaped beam regions. This results in a stress orstress gradient that can lead to the expansion of the U-shaped beamregions. The expansion of the U-shaped beam regions results in thebending of the end of beam towards the opposing beam.

In some other implementations, the stress or stress gradient isintroduced by coupling a part of the second portion of the beam toanother surface that is under mechanical stress. For example, in somemanufacturing processes, material that is deposited on a surface that isparallel to an underlying substrate may develop mechanical stress orstress gradient within the plane of the surface. This stress or stressgradient can cause the surface to expand in a direction that is parallelto the substrate. By coupling the surface to the second portion of thebeam, the expansion of the surface can cause the beam to bend towardsthe opposing beam.

Particular implementations of the subject matter described in thisdisclosure can be implemented to realize one or more of the followingpotential advantages. By introducing a mechanical stress or stressgradient in a portion of a drive beam electrode of an actuator, atip-gap between the drive beam electrode and an opposing load beamelectrode can be reduced. This reduction in the tip-gap allows areduction in an actuation voltage needed to actuate a shutter assemblythat includes the actuator. In some implementations, the reduction inthe actuation voltage can be up to about 50%. The reduction in actuationvoltage allows a reduction in the power needed to operate the shutterassembly.

FIG. 1A shows a schematic diagram of a direct-view MEMS-based displayapparatus 100. The display apparatus 100 includes a plurality of lightmodulators 102 a-102 d (generally “light modulators 102”) arranged inrows and columns. In the display apparatus 100, the light modulators 102a and 102 d are in the open state, allowing light to pass. The lightmodulators 102 b and 102 c are in the closed state, obstructing thepassage of light. By selectively setting the states of the lightmodulators 102 a-102 d, the display apparatus 100 can be utilized toform an image 104 for a backlit display, if illuminated by a lamp orlamps 105. In another implementation, the apparatus 100 may form animage by reflection of ambient light originating from the front of theapparatus. In another implementation, the apparatus 100 may form animage by reflection of light from a lamp or lamps positioned in thefront of the display, i.e., by use of a front light.

In some implementations, each light modulator 102 corresponds to a pixel106 in the image 104. In some other implementations, the displayapparatus 100 may utilize a plurality of light modulators to form apixel 106 in the image 104. For example, the display apparatus 100 mayinclude three color-specific light modulators 102. By selectivelyopening one or more of the color-specific light modulators 102corresponding to a particular pixel 106, the display apparatus 100 cangenerate a color pixel 106 in the image 104. In another example, thedisplay apparatus 100 includes two or more light modulators 102 perpixel 106 to provide luminance level in an image 104. With respect to animage, a “pixel” corresponds to the smallest picture element defined bythe resolution of image. With respect to structural components of thedisplay apparatus 100, the term “pixel” refers to the combinedmechanical and electrical components utilized to modulate the light thatforms a single pixel of the image.

The display apparatus 100 is a direct-view display in that it may notinclude imaging optics typically found in projection applications. In aprojection display, the image formed on the surface of the displayapparatus is projected onto a screen or onto a wall. The displayapparatus is substantially smaller than the projected image. In a directview display, the user sees the image by looking directly at the displayapparatus, which contains the light modulators and optionally abacklight or front light for enhancing brightness and/or contrast seenon the display.

Direct-view displays may operate in either a transmissive or reflectivemode. In a transmissive display, the light modulators filter orselectively block light which originates from a lamp or lamps positionedbehind the display. The light from the lamps is optionally injected intoa lightguide or “backlight” so that each pixel can be uniformlyilluminated. Transmissive direct-view displays are often built ontotransparent or glass substrates to facilitate a sandwich assemblyarrangement where one substrate, containing the light modulators, ispositioned directly on top of the backlight.

Each light modulator 102 can include a shutter 108 and an aperture 109.To illuminate a pixel 106 in the image 104, the shutter 108 ispositioned such that it allows light to pass through the aperture 109towards a viewer. To keep a pixel 106 unlit, the shutter 108 ispositioned such that it obstructs the passage of light through theaperture 109. The aperture 109 is defined by an opening patternedthrough a reflective or light-absorbing material in each light modulator102.

The display apparatus also includes a control matrix connected to thesubstrate and to the light modulators for controlling the movement ofthe shutters. The control matrix includes a series of electricalinterconnects (such as interconnects 110, 112 and 114), including atleast one write-enable interconnect 110 (also referred to as a“scan-line interconnect”) per row of pixels, one data interconnect 112for each column of pixels, and one common interconnect 114 providing acommon voltage to all pixels, or at least to pixels from both multiplecolumns and multiples rows in the display apparatus 100. In response tothe application of an appropriate voltage (the “write-enabling voltage,VWE”), the write-enable interconnect 110 for a given row of pixelsprepares the pixels in the row to accept new shutter movementinstructions. The data interconnects 112 communicate the new movementinstructions in the form of data voltage pulses. The data voltage pulsesapplied to the data interconnects 112, in some implementations, directlycontribute to an electrostatic movement of the shutters. In some otherimplementations, the data voltage pulses control switches, such astransistors or other non-linear circuit elements that control theapplication of separate actuation voltages, which are typically higherin magnitude than the data voltages, to the light modulators 102. Theapplication of these actuation voltages then results in theelectrostatic driven movement of the shutters 108.

FIG. 1B shows an example of a block diagram of a host device 120 (i.e.,cell phone, smart phone, PDA, MP3 player, tablet, e-reader, netbook,notebook, etc.). The host device 120 includes a display apparatus 128, ahost processor 122, environmental sensors 124, a user input module 126,and a power source.

The display apparatus 128 includes a plurality of scan drivers 130 (alsoreferred to as “write enabling voltage sources”), a plurality of datadrivers 132 (also referred to as “data voltage sources”), a controller134, common drivers 138, lamps 140-146, lamp drivers 148 and an array150 of display elements, such as the light modulators 102 shown in FIG.1A. The scan drivers 130 apply write enabling voltages to scan-lineinterconnects 110. The data drivers 132 apply data voltages to the datainterconnects 112.

In some implementations of the display apparatus, the data drivers 132are configured to provide analog data voltages to the array 150 ofdisplay elements, especially where the luminance level of the image 104is to be derived in analog fashion. In analog operation, the lightmodulators 102 are designed such that when a range of intermediatevoltages is applied through the data interconnects 112, there results arange of intermediate open states in the shutters 108 and therefore arange of intermediate illumination states or luminance levels in theimage 104. In other cases, the data drivers 132 are configured to applyonly a reduced set of 2, 3 or 4 digital voltage levels to the datainterconnects 112. These voltage levels are designed to set, in digitalfashion, an open state, a closed state, or other discrete state to eachof the shutters 108.

The scan drivers 130 and the data drivers 132 are connected to a digitalcontroller circuit 134 (also referred to as the “controller 134”). Thecontroller sends data to the data drivers 132 in a mostly serialfashion, organized in sequences, which in some implementations may bepredetermined, grouped by rows and by image frames. The data drivers 132can include series to parallel data converters, level shifting, and forsome applications digital to analog voltage converters.

The display apparatus optionally includes a set of common drivers 138,also referred to as common voltage sources. In some implementations, thecommon drivers 138 provide a DC common potential to all display elementswithin the array 150 of display elements, for instance by supplyingvoltage to a series of common interconnects 114. In some otherimplementations, the common drivers 138, following commands from thecontroller 134, issue voltage pulses or signals to the array 150 ofdisplay elements, for instance global actuation pulses which are capableof driving and/or initiating simultaneous actuation of all displayelements in multiple rows and columns of the array 150.

All of the drivers (such as scan drivers 130, data drivers 132 andcommon drivers 138) for different display functions aretime-synchronized by the controller 134. Timing commands from thecontroller coordinate the illumination of red, green and blue and whitelamps (140, 142, 144 and 146 respectively) via lamp drivers 148, thewrite-enabling and sequencing of specific rows within the array 150 ofdisplay elements, the output of voltages from the data drivers 132, andthe output of voltages that provide for display element actuation. Insome implementations, the lamps are light emitting diodes (LEDs).

The controller 134 determines the sequencing or addressing scheme bywhich each of the shutters 108 can be re-set to the illumination levelsappropriate to a new image 104. New images 104 can be set at periodicintervals. For instance, for video displays, the color images 104 orframes of video are refreshed at frequencies ranging from 10 to 300Hertz (Hz). In some implementations the setting of an image frame to thearray 150 is synchronized with the illumination of the lamps 140, 142,144 and 146 such that alternate image frames are illuminated with analternating series of colors, such as red, green, and blue. The imageframes for each respective color is referred to as a color subframe. Inthis method, referred to as the field sequential color method, if thecolor subframes are alternated at frequencies in excess of 20 Hz, thehuman brain will average the alternating frame images into theperception of an image having a broad and continuous range of colors. Inalternate implementations, four or more lamps with primary colors can beemployed in display apparatus 100, employing primaries other than red,green, and blue.

In some implementations, where the display apparatus 100 is designed forthe digital switching of shutters 108 between open and closed states,the controller 134 forms an image by the method of time division grayscale, as previously described. In some other implementations, thedisplay apparatus 100 can provide gray scale through the use of multipleshutters 108 per pixel.

In some implementations, the data for an image state 104 is loaded bythe controller 134 to the display element array 150 by a sequentialaddressing of individual rows, also referred to as scan lines. For eachrow or scan line in the sequence, the scan driver 130 applies awrite-enable voltage to the write enable interconnect 110 for that rowof the array 150, and subsequently the data driver 132 supplies datavoltages, corresponding to desired shutter states, for each column inthe selected row. This process repeats until data has been loaded forall rows in the array 150. In some implementations, the sequence ofselected rows for data loading is linear, proceeding from top to bottomin the array 150. In some other implementations, the sequence ofselected rows is pseudo-randomized, in order to minimize visualartifacts. And in some other implementations the sequencing is organizedby blocks, where, for a block, the data for only a certain fraction ofthe image state 104 is loaded to the array 150, for instance byaddressing only every 5th row of the array 150 in sequence.

In some implementations, the process for loading image data to the array150 is separated in time from the process of actuating the displayelements in the array 150. In these implementations, the display elementarray 150 may include data memory elements for each display element inthe array 150 and the control matrix may include a global actuationinterconnect for carrying trigger signals, from common driver 138, toinitiate simultaneous actuation of shutters 108 according to data storedin the memory elements.

In alternative implementations, the array 150 of display elements andthe control matrix that controls the display elements may be arranged inconfigurations other than rectangular rows and columns. For example, thedisplay elements can be arranged in hexagonal arrays or curvilinear rowsand columns. In general, as used herein, the term scan-line shall referto any plurality of display elements that share a write-enablinginterconnect.

The host processor 122 generally controls the operations of the host.For example, the host processor 122 may be a general or special purposeprocessor for controlling a portable electronic device. With respect tothe display apparatus 128, included within the host device 120, the hostprocessor 122 outputs image data as well as additional data about thehost. Such information may include data from environmental sensors, suchas ambient light or temperature; information about the host, including,for example, an operating mode of the host or the amount of powerremaining in the host's power source; information about the content ofthe image data; information about the type of image data; and/orinstructions for display apparatus for use in selecting an imaging mode.

The user input module 126 conveys the personal preferences of the userto the controller 134, either directly, or via the host processor 122.In some implementations, the user input module 126 is controlled bysoftware in which the user programs personal preferences such as “deepercolor,” “better contrast,” “lower power,” “increased brightness,”“sports,” “live action,” or “animation.” In some other implementations,these preferences are input to the host using hardware, such as a switchor dial. The plurality of data inputs to the controller 134 direct thecontroller to provide data to the various drivers 130, 132, 138 and 148which correspond to optimal imaging characteristics.

An environmental sensor module 124 also can be included as part of thehost device 120. The environmental sensor module 124 receives data aboutthe ambient environment, such as temperature and or ambient lightingconditions. The sensor module 124 can be programmed to distinguishwhether the device is operating in an indoor or office environmentversus an outdoor environment in bright daylight versus an outdoorenvironment at nighttime. The sensor module 124 communicates thisinformation to the display controller 134, so that the controller 134can optimize the viewing conditions in response to the ambientenvironment.

FIG. 2 shows an example perspective view of an illustrativeshutter-based light modulator 200. The shutter-based light modulator 200is suitable for incorporation into the direct-view MEMS-based displayapparatus 100 of FIG. 1A. The light modulator 200 includes a shutter 202coupled to an actuator 204. The actuator 204 can be formed from twoseparate compliant electrode beam actuators 205 (the “actuators 205”).The shutter 202 couples on one side to the actuators 205. The actuators205 move the shutter 202 transversely over a substrate 203 in a plane ofmotion which is substantially parallel to the substrate 203. Theopposite side of the shutter 202 couples to a spring 207 which providesa restoring force opposing the forces exerted by the actuator 204.

Each actuator 205 includes a compliant load beam 206 connecting theshutter 202 to a load anchor 208. The load anchors 208 along with thecompliant load beams 206 serve as mechanical supports, keeping theshutter 202 suspended proximate to the substrate 203. The substrate 203includes one or more aperture holes 211 for admitting the passage oflight. The load anchors 208 physically connect the compliant load beams206 and the shutter 202 to the substrate 203 and electrically connectthe load beams 206 to a bias voltage, in some instances, ground.

If the substrate 203 is opaque, such as silicon, then aperture holes 211are formed in the substrate 203 by etching an array of holes through thesubstrate 203. If the substrate 203 is transparent, such as glass orplastic, then the aperture holes 211 are formed in a layer oflight-blocking material deposited on the substrate 203. The apertureholes 211 can be generally circular, elliptical, polygonal, serpentine,or irregular in shape.

Each actuator 204 also includes a compliant drive beam 216 positionedadjacent to each load beam 206. The drive beams 216 couple at one end toa drive beam anchor 218 shared between the drive beams 216. The otherend of each drive beam 216 is free to move. Each drive beam 216 iscurved such that it is closest to the load beam 206 near the free end ofthe drive beam 216 and the anchored end of the load beam 206.

In operation, a display apparatus incorporating the light modulator 200applies an electric potential to the drive beams 216 via the drive beamanchor 218. A second electric potential may be applied to the load beams206. The resulting potential difference between the drive beams 216 andthe load beams 206 pulls the free ends of the drive beams 216 towardsthe anchored ends of the load beams 206, and pulls the shutter ends ofthe load beams 206 toward the anchored ends of the drive beams 216,thereby driving the shutter 202 transversely toward the drive beamanchor 218. The compliant load beams 206 act as springs, such that whenthe voltage across the beams 206 and 216 potential is removed, the loadbeams 206 push the shutter 202 back into its initial position, releasingthe stress stored in the load beams 206.

A light modulator, such as the light modulator 200, incorporates apassive restoring force, such as a spring, for returning a shutter toits rest position after voltages have been removed. Other shutterassemblies can incorporate a dual set of “open” and “closed” actuatorsand separate sets of “open” and “closed” electrodes for moving theshutter into either an open or a closed state.

There are a variety of methods by which an array of shutters andapertures can be controlled via a control matrix to produce images, inmany cases moving images, with appropriate luminance levels. In somecases, control is accomplished by means of a passive matrix array of rowand column interconnects connected to driver circuits on the peripheryof the display. In other cases, it is appropriate to include switchingand/or data storage elements within each pixel of the array (theso-called active matrix) to improve the speed, the luminance leveland/or the power dissipation performance of the display.

FIG. 3A shows an example schematic diagram of a control matrix 300. Thecontrol matrix 300 is suitable for controlling the light modulatorsincorporated into the MEMS-based display apparatus 100 of FIG. 1A. FIG.3B shows an example perspective view of an array 320 of shutter-basedlight modulators connected to the control matrix 300 of FIG. 3A. Thecontrol matrix 300 may address an array of pixels 320 (the “array 320”).Each pixel 301 can include an elastic shutter assembly 302, such as theshutter assembly 200 of FIG. 2, controlled by an actuator 303. Eachpixel also can include an aperture layer 322 that includes apertures324.

The control matrix 300 is fabricated as a diffused orthin-film-deposited electrical circuit on the surface of a substrate 304on which the shutter assemblies 302 are formed. The control matrix 300includes a scan-line interconnect 306 for each row of pixels 301 in thecontrol matrix 300 and a data-interconnect 308 for each column of pixels301 in the control matrix 300. Each scan-line interconnect 306electrically connects a write-enabling voltage source 307 to the pixels301 in a corresponding row of pixels 301. Each data interconnect 308electrically connects a data voltage source 309 (“Vd source”) to thepixels 301 in a corresponding column of pixels. In the control matrix300, the Vd source 309 provides the majority of the energy to be usedfor actuation of the shutter assemblies 302. Thus, the data voltagesource, Vd source 309, also serves as an actuation voltage source.

Referring to FIGS. 3A and 3B, for each pixel 301 or for each shutterassembly 302 in the array of pixels 320, the control matrix 300 includesa transistor 310 and a capacitor 312. The gate of each transistor 310 iselectrically connected to the scan-line interconnect 306 of the row inthe array 320 in which the pixel 301 is located. The source of eachtransistor 310 is electrically connected to its corresponding datainterconnect 308. The actuators 303 of each shutter assembly 302 includetwo electrodes. The drain of each transistor 310 is electricallyconnected in parallel to one electrode of the corresponding capacitor312 and to one of the electrodes of the corresponding actuator 303. Theother electrode of the capacitor 312 and the other electrode of theactuator 303 in shutter assembly 302 are connected to a common or groundpotential. In alternate implementations, the transistors 310 can bereplaced with semiconductor diodes and or metal-insulator-metal sandwichtype switching elements.

In operation, to form an image, the control matrix 300 write-enableseach row in the array 320 in a sequence by applying Vwe to eachscan-line interconnect 306 in turn. For a write-enabled row, theapplication of Vwe to the gates of the transistors 310 of the pixels 301in the row allows the flow of current through the data interconnects 308through the transistors 310 to apply a potential to the actuator 303 ofthe shutter assembly 302. While the row is write-enabled, data voltagesVd are selectively applied to the data interconnects 308. Inimplementations providing analog gray scale, the data voltage applied toeach data interconnect 308 is varied in relation to the desiredbrightness of the pixel 301 located at the intersection of thewrite-enabled scan-line interconnect 306 and the data interconnect 308.In implementations providing digital control schemes, the data voltageis selected to be either a relatively low magnitude voltage (i.e., avoltage near ground) or to meet or exceed Vat (the actuation thresholdvoltage). In response to the application of Vat to a data interconnect308, the actuator 303 in the corresponding shutter assembly actuates,opening the shutter in that shutter assembly 302. The voltage applied tothe data interconnect 308 remains stored in the capacitor 312 of thepixel 301 even after the control matrix 300 ceases to apply Vwe to arow. Therefore, the voltage Vwe does not have to wait and hold on a rowfor times long enough for the shutter assembly 302 to actuate; suchactuation can proceed after the write-enabling voltage has been removedfrom the row. The capacitors 312 also function as memory elements withinthe array 320, storing actuation instructions for the illumination of animage frame.

The pixels 301 as well as the control matrix 300 of the array 320 areformed on a substrate 304. The array 320 includes an aperture layer 322,disposed on the substrate 304, which includes a set of apertures 324 forrespective pixels 301 in the array 320. The apertures 324 are alignedwith the shutter assemblies 302 in each pixel. In some implementations,the substrate 304 is made of a transparent material, such as glass orplastic. In some other implementations, the substrate 304 is made of anopaque material, but in which holes are etched to form the apertures324.

The shutter assembly 302 together with the actuator 303 can be madebi-stable. That is, the shutters can exist in at least two equilibriumpositions (such as open or closed) with little or no power required tohold them in either position. More particularly, the shutter assembly302 can be mechanically bi-stable. Once the shutter of the shutterassembly 302 is set in position, no electrical energy or holding voltageis required to maintain that position. The mechanical stresses on thephysical elements of the shutter assembly 302 can hold the shutter inplace.

The shutter assembly 302 together with the actuator 303 also can be madeelectrically bi-stable. In an electrically bi-stable shutter assembly,there exists a range of voltages below the actuation voltage of theshutter assembly, which if applied to a closed actuator (with theshutter being either open or closed), holds the actuator closed and theshutter in position, even if an opposing force is exerted on theshutter. The opposing force may be exerted by a spring such as thespring 207 in the shutter-based light modulator 200 depicted in FIG. 2,or the opposing force may be exerted by an opposing actuator, such as an“open” or “closed” actuator.

The light modulator array 320 is depicted as having a single MEMS lightmodulator per pixel. Other implementations are possible in whichmultiple MEMS light modulators are provided in each pixel, therebyproviding the possibility of more than just binary “on’ or “off” opticalstates in each pixel. Certain forms of coded area division gray scaleare possible where multiple MEMS light modulators in the pixel areprovided, and where apertures 324, which are associated with each of thelight modulators, have unequal areas.

FIGS. 4A and 4B show example views of a dual actuator shutter assembly400. The dual actuator shutter assembly 400, as depicted in FIG. 4A, isin an open state. FIG. 4B shows the dual actuator shutter assembly 400in a closed state. In contrast to the shutter assembly 200, the shutterassembly 400 includes actuators 402 and 404 on either side of a shutter406. Each actuator 402 and 404 is independently controlled. A firstactuator, a shutter-open actuator 402, serves to open the shutter 406. Asecond opposing actuator, the shutter-close actuator 404, serves toclose the shutter 406. Both of the actuators 402 and 404 are compliantbeam electrode actuators. The actuators 402 and 404 open and close theshutter 406 by driving the shutter 406 substantially in a plane parallelto an aperture layer 407 over which the shutter is suspended. Theshutter 406 is suspended a short distance over the aperture layer 407 byanchors 408 attached to the actuators 402 and 404. The inclusion ofsupports attached to both ends of the shutter 406 along its axis ofmovement reduces out of plane motion of the shutter 406 and confines themotion substantially to a plane parallel to the substrate. By analogy tothe control matrix 300 of FIG. 3A, a control matrix suitable for usewith the shutter assembly 400 might include one transistor and onecapacitor for each of the opposing shutter-open and shutter-closeactuators 402 and 404.

The shutter 406 includes two shutter apertures 412 through which lightcan pass. The aperture layer 407 includes a set of three apertures 409.In FIG. 4A, the shutter assembly 400 is in the open state and, as such,the shutter-open actuator 402 has been actuated, the shutter-closeactuator 404 is in its relaxed position, and the centerlines of theshutter apertures 412 coincide with the centerlines of two of theaperture layer apertures 409. In FIG. 4B, the shutter assembly 400 hasbeen moved to the closed state and, as such, the shutter-open actuator402 is in its relaxed position, the shutter-close actuator 404 has beenactuated, and the light blocking portions of the shutter 406 are now inposition to block transmission of light through the apertures 409(depicted as dotted lines).

Each aperture has at least one edge around its periphery. For example,the rectangular apertures 409 have four edges. In alternativeimplementations in which circular, elliptical, oval, or other curvedapertures are formed in the aperture layer 407, each aperture may haveonly a single edge. In some other implementations, the apertures neednot be separated or disjoint in the mathematical sense, but instead canbe connected. That is to say, while portions or shaped sections of theaperture may maintain a correspondence to each shutter, several of thesesections may be connected such that a single continuous perimeter of theaperture is shared by multiple shutters.

In order to allow light with a variety of exit angles to pass throughapertures 412 and 409 in the open state, it is advantageous to provide awidth or size for shutter apertures 412 which is larger than acorresponding width or size of apertures 409 in the aperture layer 407.In order to effectively block light from escaping in the closed state,it is preferable that the light blocking portions of the shutter 406overlap the apertures 409. FIG. 4B shows an overlap 416, which can bepredefined, between the edge of light blocking portions in the shutter406 and one edge of the aperture 409 formed in the aperture layer 407.

The electrostatic actuators 402 and 404 are designed so that theirvoltage-displacement behavior provides a bi-stable characteristic to theshutter assembly 400. For each of the shutter-open and shutter-closeactuators there exists a range of voltages below the actuation voltage,which if applied while that actuator is in the closed state (with theshutter being either open or closed), will hold the actuator closed andthe shutter in position, even after an actuation voltage is applied tothe opposing actuator. The minimum voltage needed to maintain ashutter's position against such an opposing force is referred to as amaintenance voltage Vm.

FIG. 5 shows an example cross sectional view of a display apparatus 500incorporating shutter-based light modulators (shutter assemblies) 502.Each shutter assembly 502 incorporates a shutter 503 and an anchor 505.Not shown are the compliant beam actuators which, when connected betweenthe anchors 505 and the shutters 503, help to suspend the shutters 503 ashort distance above the surface. The shutter assemblies 502 aredisposed on a transparent substrate 504, such a substrate made ofplastic or glass. A rear-facing reflective layer or reflective film 506,disposed on the substrate 504 defines a plurality of surface apertures508 located beneath the closed positions of the shutters 503 of theshutter assemblies 502. The reflective film 506 reflects light notpassing through the surface apertures 508 back towards the rear of thedisplay apparatus 500. The reflective film 506 can be a fine-grainedmetal film without inclusions formed in thin film fashion by a number ofvapor deposition techniques including sputtering, evaporation, ionplating, laser ablation, or chemical vapor deposition (CVD). In someother implementations, the reflective film 506 can be formed from amirror, such as a dielectric mirror. A dielectric mirror can befabricated as a stack of dielectric thin films which alternate betweenmaterials of high and low refractive index. The vertical gap whichseparates the shutters 503 from the reflective film 506, within whichthe shutter is free to move, is in the range of 0.5 to 10 microns. Themagnitude of the vertical gap is preferably less than the lateraloverlap between the edge of shutters 503 and the edge of apertures 508in the closed state, such as the overlap 416 depicted in FIG. 4B.

The display apparatus 500 includes an optional diffuser 512 and/or anoptional brightness enhancing film 514 which separate the substrate 504from a planar light guide 516. The light guide 516 includes atransparent, i.e., glass or plastic material. The light guide 516 isilluminated by one or more light sources 518, forming a backlight. Thelight sources 518 can be, for example, and without limitation,incandescent lamps, fluorescent lamps, lasers or light emitting diodes(LEDs). A reflector 519 helps direct light from lamp 518 towards thelight guide 516. A front-facing reflective film 520 is disposed behindthe backlight 516, reflecting light towards the shutter assemblies 502.Light rays such as ray 521 from the backlight that do not pass throughone of the shutter assemblies 502 will be returned to the backlight andreflected again from the film 520. In this fashion light that fails toleave the display apparatus 500 to form an image on the first pass canbe recycled and made available for transmission through other openapertures in the array of shutter assemblies 502. Such light recyclinghas been shown to increase the illumination efficiency of the display.

The light guide 516 includes a set of geometric light redirectors orprisms 517 which re-direct light from the lamps 518 towards theapertures 508 and hence toward the front of the display. The lightredirectors 517 can be molded into the plastic body of light guide 516with shapes that can be alternately triangular, trapezoidal, or curvedin cross section. The density of the prisms 517 generally increases withdistance from the lamp 518.

In some implementations, the reflective film 506 can be made of a lightabsorbing material, and in alternate implementations the surfaces ofshutter 503 can be coated with either a light absorbing or a lightreflecting material. In some other implementations, the reflective film506 can be deposited directly on the surface of the light guide 516. Insome implementations, the reflective film 506 need not be disposed onthe same substrate as the shutters 503 and anchors 505 (such as in theMEMS-down configuration described below).

In some implementations, the light sources 518 can include lamps ofdifferent colors, for instance, the colors red, green and blue. A colorimage can be formed by sequentially illuminating images with lamps ofdifferent colors at a rate sufficient for the human brain to average thedifferent colored images into a single multi-color image. The variouscolor-specific images are formed using the array of shutter assemblies502. In another implementation, the light source 518 includes lampshaving more than three different colors. For example, the light source518 may have red, green, blue and white lamps, or red, green, blue andyellow lamps. In some other implementations, the light source 518 mayinclude cyan, magenta, yellow and white lamps, red, green, blue andwhite lamps. In some other implementations, additional lamps may beincluded in the light source 518. For example, if using five colors, thelight source 518 may include red, green, blue, cyan and yellow lamps. Insome other implementations, the light source 518 may include white,orange, blue, purple and green lamps or white, blue, yellow, red andcyan lamps. If using six colors, the light source 518 may include red,green, blue, cyan, magenta and yellow lamps or white, cyan, magenta,yellow, orange and green lamps.

A cover plate 522 forms the front of the display apparatus 500. The rearside of the cover plate 522 can be covered with a black matrix 524 toincrease contrast. In alternate implementations the cover plate includescolor filters, for instance distinct red, green, and blue filterscorresponding to different ones of the shutter assemblies 502. The coverplate 522 is supported a distance away, which in some implementationsmay be predetermined, from the shutter assemblies 502 forming a gap 526.The gap 526 is maintained by mechanical supports or spacers 527 and/orby an adhesive seal 528 attaching the cover plate 522 to the substrate504.

The adhesive seal 528 seals in a fluid 530. The fluid 530 is engineeredwith viscosities preferably below about 10 centipoise and with relativedielectric constant preferably above about 2.0, and dielectric breakdownstrengths above about 104 V/cm. The fluid 530 also can serve as alubricant. In some implementations, the fluid 530 is a hydrophobicliquid with a high surface wetting capability. In alternateimplementations, the fluid 530 has a refractive index that is eithergreater than or less than that of the substrate 504.

Displays that incorporate mechanical light modulators can includehundreds, thousands, or in some cases, millions of moving elements. Insome devices, every movement of an element provides an opportunity forstatic friction to disable one or more of the elements. This movement isfacilitated by immersing all the parts in a fluid (also referred to asfluid 530) and sealing the fluid (such as with an adhesive) within afluid space or gap in a MEMS display cell. The fluid 530 is usually onewith a low coefficient of friction, low viscosity, and minimaldegradation effects over the long term. When the MEMS-based displayassembly includes a liquid for the fluid 530, the liquid at leastpartially surrounds some of the moving parts of the MEMS-based lightmodulator. In some implementations, in order to reduce the actuationvoltages, the liquid has a viscosity below 70 centipoise. In some otherimplementations, the liquid has a viscosity below 10 centipoise. Liquidswith viscosities below 70 centipoise can include materials with lowmolecular weights: below 4000 grams/mole, or in some cases below 400grams/mole. Fluids 530 that also may be suitable for suchimplementations include, without limitation, de-ionized water, methanol,ethanol and other alcohols, paraffins, olefins, ethers, silicone oils,fluorinated silicone oils, or other natural or synthetic solvents orlubricants. Useful fluids can be polydimethylsiloxanes (PDMS), such ashexamethyldisiloxane and octamethyltrisiloxane, or alkyl methylsiloxanes such as hexylpentamethyldisiloxane. Useful fluids can bealkanes, such as octane or decane. Useful fluids can be nitroalkanes,such as nitromethane. Useful fluids can be aromatic compounds, such astoluene or diethylbenzene. Useful fluids can be ketones, such asbutanone or methyl isobutyl ketone. Useful fluids can be chlorocarbons,such as chlorobenzene. Useful fluids can be chlorofluorocarbons, such asdichlorofluoroethane or chlorotrifluoroethylene. Other fluids consideredfor these display assemblies include butyl acetate anddimethylformamide. Still other useful fluids for these displays includehydro fluoro ethers, perfluoropolyethers, hydro fluoro poly ethers,pentanol, and butanol. Example suitable hydro fluoro ethers includeethyl nonafluorobutyl ether and2-trifluoromethyl-3-ethoxydodecafluorohexane.

A sheet metal or molded plastic assembly bracket 532 holds the coverplate 522, the substrate 504, the backlight and the other componentparts together around the edges. The assembly bracket 532 is fastenedwith screws or indent tabs to add rigidity to the combined displayapparatus 500. In some implementations, the light source 518 is moldedin place by an epoxy potting compound. Reflectors 536 help return lightescaping from the edges of the light guide 516 back into the light guide516. Not depicted in FIG. 5 are electrical interconnects which providecontrol signals as well as power to the shutter assemblies 502 and thelamps 518.

In some other implementations, the roller-based light modulator 220, thelight tap 250, or the electrowetting-based light modulation array 270,as depicted in FIGS. 2A-2D, as well as other MEMS-based lightmodulators, can be substituted for the shutter assemblies 502 within thedisplay apparatus 500.

The display apparatus 500 is referred to as the MEMS-up configuration,where the MEMS based light modulators are formed on a front surface ofthe substrate 504, i.e., the surface that faces toward the viewer. Theshutter assemblies 502 are built directly on top of the reflective film506. In an alternate implementation, referred to as the MEMS-downconfiguration, the shutter assemblies are disposed on a substrateseparate from the substrate on which the reflective aperture layer isformed. The substrate on which the reflective aperture layer is formed,defining a plurality of apertures, is referred to herein as the apertureplate. In the MEMS-down configuration, the substrate that carries theMEMS-based light modulators takes the place of the cover plate 522 inthe display apparatus 500 and is oriented such that the MEMS-based lightmodulators are positioned on the rear surface of the top substrate,i.e., the surface that faces away from the viewer and toward the lightguide 516. The MEMS-based light modulators are thereby positioneddirectly opposite to and across a gap from the reflective film 506. Thegap can be maintained by a series of spacer posts connecting theaperture plate and the substrate on which the MEMS modulators areformed. In some implementations, the spacers are disposed within orbetween each pixel in the array. The gap or distance that separates theMEMS light modulators from their corresponding apertures is preferablyless than 10 microns, or a distance that is less than the overlapbetween shutters and apertures, such as overlap 416.

FIGS. 6A-6E show cross sectional views of stages of construction of anexample composite shutter assembly. FIG. 6A shows an example crosssectional diagram of a completed composite shutter assembly 600. Theshutter assembly 600 includes a shutter 601, two compliant beams 602,and an anchor structure 604 built-up on a substrate 603 and an aperturelayer 606. The elements of the composite shutter assembly 600 include afirst mechanical layer 605, a conductor layer 607, a second mechanicallayer 609, and an encapsulating dielectric 611. At least one of themechanical layers 605 or 609 can be deposited to thicknesses in excessof 0.15 microns, as one or both of the mechanical layers 605 or 609serves as the principal load bearing and mechanical actuation member forthe shutter assembly 600, though in some implementations, the mechanicallayers 605 and 609 may be thinner. Candidate materials for themechanical layers 605 and 609 include, without limitation, metals suchas aluminum (Al), copper (Cu), nickel (Ni), chromium (Cr), molybdenum(Mo), titanium (Ti), tantalum (Ta), niobium (Nb), neodymium (Nd), oralloys thereof; dielectric materials such as aluminum oxide (Al₂O₃),silicon oxide (SiO₂), tantalum pentoxide (Ta₂O₅), or silicon nitride(Si₃N₄); or semiconducting materials such as diamond-like carbon,silicon (Si), germanium (Ge), gallium arsenide (GaAs), cadmium telluride(CdTe) or alloys thereof. At least one of the layers, such as theconductor layer 607, should be electrically conducting so as to carrycharge on to and off of the actuation elements. Candidate materialsinclude, without limitation, Al, Cu, Ni, Cr, Mo, Ti, Ta, Nb, Nd, oralloys thereof or semiconducting materials such as diamond-like carbon,Si, Ge, GaAs, CdTe or alloys thereof. In some implementations employingsemiconductor layers, the semiconductors are doped with impurities suchas phosphorus (P), arsenic (As), boron (B), or Al. FIG. 6A depicts asandwich configuration for the composite in which the mechanical layers605 and 609, having similar thicknesses and mechanical properties, aredeposited on either side of the conductor layer 607. In someimplementations, the sandwich structure helps to ensure that stressesremaining after deposition and/or stresses that are imposed bytemperature variations will not act to cause bending, warping or otherdeformation of the shutter assembly 600.

In some implementations, the order of the layers in the compositeshutter assembly 600 can be inverted, such that the outside of theshutter assembly 600 is formed from a conductor layer while the insideof the shutter assembly 600 is formed from a mechanical layer.

The shutter assembly 600 can include an encapsulating dielectric 611. Insome implementations, dielectric coatings can be applied in conformalfashion, such that all exposed bottom, top, and side surfaces of theshutter 601, the anchor 604, and the beams 602 are uniformly coated.Such thin films can be grown by thermal oxidation and/or by conformalCVD of an insulator such as Al₂O₃, chromium (III) oxide (Cr₂O₃),titanium oxide (TiO₂), hafnium oxide (HfO₂), vanadium oxide (V₂O₅),niobium oxide (Nb₂O₅), Ta₂O₅, SiO₂, or Si₃N₄, or by depositing similarmaterials via atomic layer deposition. The dielectric coating layer canbe applied with thicknesses in the range of 10 nm to 1 micron. In someimplementations, sputtering and evaporation can be used to deposit thedielectric coating onto sidewalls.

FIGS. 6B-6E show example cross sectional views of the results of certainintermediate manufacturing stages of an example process used to form theshutter assembly 600 depicted in FIG. 6A. In some implementations, theshutter assembly 600 is built on top of a pre-existing control matrix,such as an active matrix array of thin film transistors, such as thecontrol matrices depicted in FIGS. 3A and 3B.

FIG. 6B shows a cross sectional view of the results of a first stage inan example process of forming the shutter assembly 600. As depicted inFIG. 6B, a sacrificial layer 613 is deposited and patterned. In someimplementations, polyimide is used as a sacrificial layer material.Other candidate sacrificial layer materials include, without limitation,polymer materials such as polyamide, fluoropolymer, benzocyclobutene,polyphenylquinoxylene, parylene, or polynorbornene. These materials arechosen for their ability to planarize rough surfaces, maintainmechanical integrity at processing temperatures in excess of 250° C.,and their ease of etch and/or thermal decomposition during removal. Inother implementations, the sacrificial layer 613 is formed from aphotoresist, such as polyvinyl acetate, polyvinyl ethylene, and phenolicor novolac resins. An alternate sacrificial layer material used in someimplementations is SiO₂, which can be removed preferentially as long asother electronic or structural layers are resistant to the hydrofluoricacid solutions used for its removal. One such suitable resistantmaterial is Si₃N₄. Another alternate sacrificial layer material is Si,which can be removed preferentially as long as electronic or structurallayers are resistant to the fluorine plasmas or xenon difluoride (XeF₂)used for its removal, such as most metals and Si₃N₄. Yet anotheralternate sacrificial layer material is Al, which can be removedpreferentially as long as other electronic or structural layers areresistant to strong base solutions, such as concentrated sodiumhydroxide (NaOH) solutions. Suitable materials include, for example, Cr,Ni, Mo, Ta and Si. Still another alternate sacrificial layer material isCu, which can be removed preferentially as long as other electronic orstructural layers are resistant to nitric or sulfuric acid solutions.Such materials include, for example, Cr, Ni, and Si.

Next the sacrificial layer 613 is patterned to expose holes or vias atthe anchor regions 604. In implementations employing polyimide or othernon-photoactive materials as the sacrificial layer material, thesacrificial layer material can be formulated to include photoactiveagents, allowing regions exposed through a UV photomask to bepreferentially removed in a developer solution. Sacrificial layersformed from other materials can be patterned by coating the sacrificiallayer 613 in an additional layer of photoresist, photopatterning thephotoresist, and finally using the photoresist as an etching mask. Thesacrificial layer 613 alternatively can be patterned by coating thesacrificial layer 613 with a hard mask, which can be a thin layer ofSiO₂ or a metal such as Cr. A photopattern is then transferred to thehard mask by way of photoresist and wet chemical etching. The patterndeveloped in the hard mask can be resistant to dry chemical,anisotropic, or plasma etching—techniques which can be used to impartdeep and narrow anchor holes into the sacrificial layer 613.

After the anchor regions 604 have been opened in the sacrificial layer613, the exposed and underlying conducting surface 614 can be etched,either chemically or via the sputtering effects of a plasma, to removeany surface oxide layers. Such a contact etching stage can improve theohmic contact between the underlying conducting surface 614 and theshutter material. After patterning of the sacrificial layer 613, anyphotoresist layers or hard masks can be removed through use of eithersolvent cleaning or acid etching.

Next, in the process for building the shutter assembly 600, as depictedin FIG. 6C, the shutter materials are deposited. The shutter assembly600 is composed of multiple thin films: the first mechanical layer 605,the conductor layer 607 and the second mechanical layer 609. In someimplementations, the first mechanical layer 605 is an amorphous silicon(a-Si) layer, the conductor layer 607 is Al and the second mechanicallayer 609 is a-Si. The first mechanical layer 605, the conductor layer607, and the second mechanical layer 609 are deposited at a temperaturewhich is below that at which physical degradation occurs for thesacrificial layer 613. For instance, polyimide decomposes attemperatures above about 400° C. Therefore, in some implementations, thefirst mechanical layer 605, the conductor layer 607 and the secondmechanical layer 609 are deposited at temperatures below about 400° C.,allowing usage of polyimide as a sacrificial layer material. In someimplementations, hydrogenated amorphous silicon (a-Si:H) is a usefulmechanical material for the first and second mechanical layers 605 and609 since it can be grown to thicknesses in the range of about 0.15 toabout 3 microns, in a relatively stress-free state, by way ofplasma-enhanced chemical vapor deposition (PECVD) from silane gas attemperatures in the range of about 250 to about 350° C. In some of suchimplementations, phosphine gas (PH₃) is used as a dopant so that thea-Si can be grown with resistivities below about 1 ohm-cm. In alternateimplementations, a similar PECVD technique can be used for thedeposition of Si₃N₄, silicon-rich Si₃N₄, or SiO₂ materials as the firstmechanical layer 605 or for the deposition of diamond-like carbon, Ge,SiGe, CdTe, or other semiconducting materials for the first mechanicallayer 605. An advantage of the PECVD deposition technique is that thedeposition can be quite conformal, that is, it can coat a variety ofinclined surfaces or the inside surfaces of narrow via holes. Even ifthe anchor or via holes which are cut into the sacrificial layermaterial present nearly vertical sidewalls, the PECVD technique canprovide a substantially continuous coating between the bottom and tophorizontal surfaces of the anchor.

In addition to the PECVD technique, alternate suitable techniquesavailable for the growth of the first and second mechanical layers 605and 609 include RF or DC sputtering, metal-organic CVD, evaporation,electroplating or electroless plating.

For the conductor layer 607, in some implementations, a metal thin film,such as Al, is utilized. In some other implementations, alternativemetals, such as Cu, Ni, Mo, or Ta can be chosen. The inclusion of such aconducting material serves two purposes. It reduces the overall sheetresistance of the shutter 601, and it helps to block the passage ofvisible light through the shutter 601, since a-Si, if less than about 2microns thick, as may be used in some implementations of the shutter601, can transmit visible light to some degree. The conducting materialcan be deposited either by sputtering or, in a more conformal fashion,by CVD techniques, electroplating, or electroless plating.

FIG. 6D shows the results of the next set of processing stages used inthe formation of the shutter assembly 600. The first mechanical layer605, the conductor layer 607, and the second mechanical layer 609 arephotomasked and etched while the sacrificial layer 613 is still on thesubstrate 603. First, a photoresist material is applied, then exposedthrough a photomask, and then developed to form an etch mask. Amorphoussilicon, Si₃N₄, and SiO₂ can then be etched in fluorine-based plasmachemistries. SiO₂ mechanical layers also can be etched using HF wetchemicals; and any metals in the conductor layer 607 can be etched witheither wet chemicals or chlorine-based plasma chemistries.

The pattern shapes applied through the photomask can influence themechanical properties, such as stiffness, compliance, and the voltageresponse in the actuator and shutter 601 of the shutter assembly 600.The shutter assembly 600 includes the compliant beams 602, shown incross section. Each compliant beam 602 is shaped such that the width isless than the total height or thickness of the shutter material. In someimplementations, the beam dimensional ratio is maintained at about 1.4:1or greater, with the compliant beams 602 being taller or thicker thanthey are wide.

The results of subsequent stages of the example manufacturing processfor building the shutter assembly 600 are depicted in FIG. 6E. Thesacrificial layer 613 is removed, which frees-up all moving parts fromthe substrate 603, except at the anchor points. In some implementations,polyimide sacrificial materials are removed in an oxygen plasma. Otherpolymer materials used for the sacrificial layer 613 also can be removedin an oxygen plasma, or in some cases by thermal pyrolysis. Somesacrificial layer materials (such as SiO₂) can be removed by wetchemical etching or by vapor phase etching.

In a final process, the results of which are depicted in FIG. 6A, theencapsulating dielectric 611 is deposited on all exposed surfaces of theshutter assembly 600. In some implementations, the encapsulatingdielectric 611 can be applied in a conformal fashion, such that allbottom, top, and side surfaces of the shutter 601 and the beams 602 areuniformly coated using CVD. In some other implementations, only the topand side surfaces of the shutter 601 are coated. In someimplementations, Al₂O₃ is used for the encapsulating dielectric 611 andis deposited by atomic layer deposition to thicknesses in the range ofabout 10 to about 100 nanometers.

Finally, anti-stiction coatings can be applied to the surfaces of theshutter 601 and the beams 602. These coatings prevent the unwantedstickiness or adhesion between two independent beams of an actuator.Suitable coatings include carbon films (both graphite and diamond-like)as well as fluoropolymers, and/or low vapor pressure lubricants, as wellas chlorosilanes, hydrocarbon chlorosilanes, fluorocarbon chlorosilanes,such as methoxy-terminated silanes, perfluoronated, amino-silanes,siloxanes and carboxylic acid based monomers and species. These coatingscan be applied by either exposure to a molecular vapor or bydecomposition of precursor compounds by way of CVD. Anti-stictioncoatings also can be created by the chemical alteration of shuttersurfaces, such as by fluoridation, silanization, siloxidation, orhydrogenation of insulating surfaces.

One class of suitable actuators for use in MEMS-based shutter displaysinclude compliant actuator beams for controlling shutter motion that istransverse to or in-the-plane of the display substrate. The voltageemployed for the actuation of such shutter assemblies decreases as theactuator beams become more compliant. The control of actuated motionalso improves if the beams are shaped such that in-plane motion ispreferred or promoted with respect to out-of-plane motion. Thus, in someimplementations, the compliant actuator beams have a rectangular crosssection, such that the beams are taller or thicker than they are wide.

The stiffness of a long rectangular beam with respect to bending withina particular plane scales with the thinnest dimension of that beam inthat plane to the third power. It is therefore advantageous to reducethe width of the compliant beams to reduce the actuation voltages forin-plane motion. When using conventional photolithography equipment todefine and fabricate the shutter and actuator structures, however, theminimum width of the beams can be limited to the resolution of theoptics. And although photolithography equipment has been developed fordefining patterns in photoresist with narrow features, such equipment isexpensive, and the areas over which patterning can be accomplished in asingle exposure are limited. For economical photolithography over largepanels of glass or other transparent substrates, the patterningresolution or minimum feature size is typically limited to severalmicrons.

FIGS. 7A-7D show isometric views of stages of construction of an exampleshutter assembly 700 with narrow sidewall beams. This alternate processyields compliant actuator beams 718 and 720 and a compliant spring beam716 (collectively referred to as “sidewall beams 716, 718 and 720”),which have a width well below the conventional lithography limits onlarge glass panels. In the process depicted in FIGS. 7A-7D, thecompliant beams of shutter assembly 700 are formed as sidewall featureson a mold made from a sacrificial material. The process is referred toas a sidewall beams process.

The process of forming the shutter assembly 700 with the sidewall beams716, 718 and 720 begins, as depicted in FIG. 7A, with the deposition andpatterning of a first sacrificial material 701. The pattern defined inthe first sacrificial material 701 creates openings or vias 702 withinwhich anchors for the shutter assembly 700 eventually will be formed.The deposition and patterning of the first sacrificial material 701 issimilar in concept, and uses similar materials and techniques, as thosedescribed for the deposition and patterning described in relation toFIGS. 6A-6E.

The process of forming the sidewall beams 716, 718 and 720 continueswith the deposition and patterning of a second sacrificial material 705.FIG. 7B shows the shape of a mold 703 that is created after patterningof the second sacrificial material 705. The mold 703 also includes thefirst sacrificial material 701 with its previously defined vias 702. Themold 703 in FIG. 7B includes two distinct horizontal levels. The bottomhorizontal level 708 of the mold 703 is established by the top surfaceof the first sacrificial layer 701 and is accessible in those areaswhere the second sacrificial material 705 has been etched away. The tophorizontal level 710 of the mold 703 is established by the top surfaceof the second sacrificial material 705. The mold 703 depicted in FIG. 7Balso includes substantially vertical sidewalls 709. Materials for use asthe first and second sacrificial materials 701 and 705 are describedabove with respect to the sacrificial layer 613 of FIGS. 6A-6E.

The process of forming the sidewall beams 716, 718 and 720 continueswith the deposition and patterning of shutter material onto all of theexposed surfaces of the sacrificial mold 703, as depicted in FIG. 7C.Suitable materials for use in forming the shutter 712 are describedabove with respect to the first mechanical layer 605, the conductorlayer 607, and the second mechanical layer 609 of FIGS. 6A-6E. Theshutter material is deposited to a thickness of less than about 2microns. In some implementations, the shutter material is deposited tohave a thickness of less than about 1.5 microns. In some otherimplementations, the shutter material is deposited to have a thicknessof less than about 1.0 microns, and as thin as about 0.10 microns. Afterdeposition, the shutter material (which may be a composite of severalmaterials as described above) is patterned, as depicted in FIG. 7C.First, a photoresist is deposited on the shutter material. Thephotoresist is then patterned. The pattern developed into thephotoresist is designed such that the shutter material, after asubsequent etch stage, remains in the region of the shutter 712 as wellas at the anchors 714.

The manufacturing process continues with applying an anisotropic etch,resulting in the structure depicted in FIG. 7C. The anisotropic etch ofthe shutter material is carried out in a plasma atmosphere with avoltage bias applied to the substrate 726 or to an electrode inproximity to the substrate 726. The biased substrate 726 (with electricfield perpendicular to the surface of the substrate 726) leads toacceleration of ions toward the substrate 726 at an angle nearlyperpendicular to the substrate 726. Such accelerated ions, coupled withthe etching chemicals, lead to etch rates that are much faster in adirection that is normal to the plane of the substrate 726 as comparedto directions parallel to the substrate 726. Undercut-etching of shuttermaterial in the regions protected by a photoresist is therebysubstantially eliminated. Along the vertical sidewalls 709 of the mold703, which are substantially parallel to the track of the acceleratedions, the shutter material also is substantially protected from theanisotropic etch. Such protected sidewall shutter material form thesidewall beams 716, 718, and 720 for supporting the shutter 712. Alongother (non-photoresist-protected) horizontal surfaces of the mold 703,such as the top horizontal surface 710 or the bottom horizontal surface708, the shutter material has been substantially completely removed bythe etch.

The anisotropic etch used to form the sidewall beams 716, 718 and 720can be achieved in either an RF or DC plasma etching device as long asprovision for electrical bias of the substrate 726 or of an electrode inclose proximity of the substrate 726 is supplied. For the case of RFplasma etching, an equivalent self-bias can be obtained by disconnectingthe substrate holder from the grounding plates of the excitationcircuit, thereby allowing the substrate potential to float in theplasma. In some implementations, it is possible to provide an etchinggas such as trifluoromethane (CHF₃), perfluorobutene (C₄F₈), orchloroform (CHCl₃) in which both carbon and hydrogen and/or carbon andfluorine are constituents in the etch gas. When coupled with adirectional plasma, achieved again through voltage biasing of thesubstrate 726, the liberated carbon (C), hydrogen (H), and/or fluorine(F) atoms can migrate to the vertical sidewalls 709 where they build upa passive or protective quasi-polymer coating. This quasi-polymercoating further protects the sidewall beams 716, 718 and 720 frometching or chemical attack.

The process of forming the sidewall beams 716, 718 and 720 includes theremoval of the remainder of the second sacrificial material 705 and thefirst sacrificial material 701. The result is shown in FIG. 7D. Theprocess of removing sacrificial material is similar to that describedwith respect to FIG. 6E. The material deposited on the verticalsidewalls 709 of the mold 703 remain as the sidewall beams 716, 718 and720. The sidewall beam 716 serves as a spring mechanically connectingthe anchors 714 to the shutter 712, and also provides a passiverestoring force and to counter the forces applied by the actuator formedfrom the compliant beams 718 and 720. The anchors 714 connect to anaperture layer 725. The sidewall beams 716, 718 and 720 are tall andnarrow. The width of the sidewall beams 716, 718 and 720, as formed fromthe surface of the mold 703, is similar to the thickness of the shuttermaterial as deposited. In some implementations, the width of sidewallbeam 716 will be the same as the thickness of shutter 712. In some otherimplementations, the beam width will be about ½ the thickness of theshutter 712. The height of the sidewall beams 716, 718 and 720 isdetermined by the thickness of the second sacrificial material 705, orin other words, by the depth of the mold 703, as created during thepatterning operation described in relation to FIG. 7B. As long as thethickness of the deposited shutter material is chosen to be less thanabout 2 microns, the process depicted in FIGS. 7A-7D is well suited forthe production of narrow beams. In fact, for many applications thethickness range of 0.1 to 2.0 micron is quite suitable. Conventionalphotolithography would limit the patterned features shown in FIGS. 7A,7B and 7C to much larger dimensions, for instance allowing minimumresolved features no smaller than 2 microns or 5 microns.

FIG. 7D depicts an isomeric view of the shutter assembly 700, formedafter the release operation in the above-described process, yieldingcompliant beams with cross sections of high aspect ratios. As long asthe thickness of the second sacrificial material 705 is, for example,greater than about 4 times larger than the thickness of the shuttermaterial, the resulting ratio of beam height to beam width will beproduced to a similar ratio, i.e., greater than about 4:1.

An optional stage, not illustrated above but included as part of theprocess leading to FIG. 7C, involves isotropic etching of the sidewallbeam material to separate or decouple the compliant load beams 720 fromthe compliant drive beams 718. For instance, the shutter material atpoint 724 has been removed from the sidewall through use of an isotropicetch. An isotropic etch is one whose etch rate is substantially the samein all directions, so that sidewall material in regions such as point724 is no longer protected. The isotropic etch can be accomplished inthe typical plasma etch equipment as long as a bias voltage is notapplied to the substrate 726. An isotropic etch also can be achievedusing wet chemical or vapor phase etching techniques. Prior to thisoptional fourth masking and etch stage, the sidewall beam materialexists essentially continuously around the perimeter of the recessedfeatures in the mold 703. The fourth mask and etch stage is used toseparate and divide the sidewall material, forming the distinct beams718 and 720. The separation of the beams 718 and 720 at point 724 isachieved through a fourth process of photoresist dispense, and exposurethrough a mask. The photoresist pattern in this case is designed toprotect the sidewall beam material against isotropic etching at allpoints except at the separation point 724.

As a final stage in the sidewall process, an encapsulating dielectric isdeposited around the outside surfaces of the sidewall beams 716, 718 and720.

In order to protect the shutter material deposited on the verticalsidewalls 709 of the mold 703 and to produce the sidewall beams 716, 718and 720 of substantially uniform cross section, some particular processguidelines can be followed. For instance, in FIG. 7B, the sidewalls 709can be made as vertical as possible. Slopes at the vertical sidewalls709 and/or exposed surfaces become susceptible to the anisotropic etch.In some implementations, the vertical sidewalls 709 can be produced bythe patterning operation at FIG. 7B, such as the patterning of thesecond sacrificial material 705 in an anisotropic fashion. The use of anadditional photoresist coating or a hard mask in conjunction withpatterning of the second sacrificial layer 705 allows the use ofaggressive plasmas and/or high substrate bias in the anisotropic etch ofthe second sacrificial material 705 while mitigating against excessivewear of the photoresist. The vertical sidewalls 709 also can be producedin photoimageable sacrificial materials as long as care is taken tocontrol the depth of focus during the UV exposure and excessiveshrinkage is avoided during final cure of the resist.

Another process guideline that helps during sidewall beam processingrelates to the conformality of the shutter material deposition. Thesurfaces of the mold 703 can be covered with similar thicknesses of theshutter material, regardless of the orientation of those surfaces,either vertical or horizontal. Such conformality can be achieved whendepositing with CVD. In particular, the following conformal techniquescan be employed: PECVD, low pressure chemical vapor deposition (LPCVD),and atomic or self-limited layer deposition (ALD). In the above CVDtechniques the growth rate of the thin film can be limited by reactionrates on a surface as opposed to exposing the surface to a directionalflux of source atoms. In some implementations, the thickness of materialgrown on vertical surfaces is at least 50% of the thickness of materialgrown on horizontal surfaces. Alternatively, shutter materials can beconformally deposited from solution by electroless plating orelectroplating, after a metal seed layer is provided that coats thesurfaces before plating.

FIGS. 8A-8C show various views of an example shutter assembly 800 havinga first tip-gap adjustment feature (TGAF). In particular, FIG. 8A showsa top view of the shutter assembly 800, FIG. 8B shows a cross-sectionalview of the first TGAF, and FIG. 8C shows a top view of the shutterassembly 800 after release, illustrating a reduction in tip-gap as aresult of the TGAF.

FIG. 8A shows the shutter assembly 800 having the first TGAF 802.Specifically, FIG. 8A shows the shutter assembly 800 at a stage ofmanufacture that precedes release of the shutter assembly 800, but thatis after the stage in which the shutter assembly 800 has been patterned.The shutter assembly 800 is supported by a sacrificial mold 804. Thesacrificial mold 804 can be similar to the second sacrificial mold 703discussed in relation to FIG. 7B above. As such, the sacrificial mold804 can also include two or more sacrificial material layers similar tothe first sacrificial layer 701 and the second sacrificial material 705also shown in FIG. 7B. The sacrificial mold 804 is patterned to formraised mold mesas that have substantially vertical sidewalls, which areutilized for forming narrow drive and load beams.

The sacrificial mold 804 includes raised portions, referred to as afirst mold mesa 806 and a second mold mesa 808. An elongated, loopeddrive beam 807 is formed on the sidewalls of the first mold mesa 806,while the load beam 809, the shutter 810 and the spring beam 812 areformed on the sidewalls and the top surface of the second mold mesa 808.A peripheral beam 813 is also provided to enclose the second mold mesa808 between the load beam 809, the spring beam 812 and the peripheralbeam 813. One end of the peripheral beam 813 is coupled to the loadanchor 822 while the other end is coupled to the spring anchor 824.

The looped drive beam 807, which is formed on the sidewalls of the firstmold mesa 806, includes a first portion 814, a second portion 816 andconnecting portion 818 that connects the first portion 814 to the secondportion 816. The first portion 814 extends away from a drive anchor 820adjacent to the load beam 809. The second portion 816, which ispositioned behind the first portion 814 with respect to the load beam809, also extends away from the drive anchor 820. The connecting portion818 is a curved portion that connects the first portion 814 and thesecond portion 816 to complete the looped drive beam 807.

The load beam 809, which is formed on the sidewall of the second moldmesa 808, extends away from a load anchor 822 and connects to theshutter 810. The load beam 809 is situated in close proximity to thelooped drive beam 807. The other end of the shutter 810 is connected tothe spring beam 812, which extends away from a spring anchor 824.

The looped drive beam 807 entirely encloses the boundary of space formedby the first mold mesa 806. Similarly, the incorporation of theperipheral beam 813 allows the combination of the load beam 809, thespring beam 812 and the peripheral beam 813 to together, entirelyenclose the boundary of space formed by the second mold mesa 808. Thisis in contrast with the drive beam 718 shown in FIG. 7C, which does notentirely enclose any portion of the mold 703. Instead, to achieve thedesired operation, the drive beam 718 requires separation from theanchor 714 at the termination region 724, all shown in FIG. 7C. Theseparation is typically achieved by an additional photolithographyprocess, which can be costly. But the shutter assembly 800 of FIG. 8Adoes not require any such separation of the looped drive beam 807 toperform its desired operation. Thus, by building the shutter assembly800 in a manner such that features of the shutter assembly 800 entirelyenclose boundaries of spaces formed by the mold 804, additional costlyphotolithography processes are avoided.

The looped drive beam 807 and the load beam 809 form an actuator 826,which when actuated, during normal operation of the shutter assembly800, results in electrostatic forces that pull the load beam 809 towardsthe looped drive beam 807. This causes the shutter 810 to movesubstantially parallel to a substrate, and towards the looped drive beam807. When the actuator 826 is relaxed, the spring beam 812 pulls theshutter 810 back in the opposite direction.

In some implementations, the shutter assembly 800 can include a secondactuator in addition to the actuator 826 shown in FIG. 8A. In suchimplementations, the second actuator, instead of the spring beam 812,can be utilized to pull the shutter 810 in a direction opposing thedirection in which the first actuator 826 pulls the shutter 810. Thesecond actuator can be similar to the actuator 826, in that the secondactuator can also include a looped drive beam and a load beam coupled tothe shutter 810 on the opposite side to which the load beam 809 iscoupled to the shutter. Furthermore, the looped drive beam of the secondactuator can also include a TGAF similar to the TGAF 802 shown on thelooped drive beam 807. The looped drive beam of the second actuator canbe formed on a mold mesa similar to the mold mesa 806 over which thelooped derive beam 807 is formed, while the load beam of the secondactuator can be formed on the sidewalls of the first mold mesa 808.Appropriate actuation and relaxation of the second actuator inconjunction with the actuation and relaxation of the actuator 826 can beused to move the shutter 810 in a desired position.

The actuator 826 is actuated by applying an actuation voltage across thelooped drive beam 807 and the load beam 809. The magnitude of theactuation voltage needed to effectively operate the shutter assembly 800is a function, in part, of the distance between the tip of the loopeddrive beam 807 and the load beam 809, also known as the tip-gap.Particularly, the actuation voltage needed decreases with a decrease inthe tip-gap. As shown in FIG. 8A, the tip-gap between the looped drivebeam 807 and the load beam 808 is indicated by the first tip-gap TG1.

The second portion 816 of the looped drive beam 807 includes the firstTGAF 802, which is utilized in reducing the first tip-gap TG1. The firstTGAF 802 includes multiple U-shaped beam regions that are formed on thesidewalls of multiple projections 806 a extending out from the firstmold mesa 806. More particularly, the TGAF 802 includes generallyU-shaped beam regions 816 a formed within narrow channels locatedbetween the projections 806 a and outer beam regions 816 b formed on theoutside of the outermost projections 806 a. Some exemplary dimensions ofthe TGAF 802 and the narrow channels between the projections 806 a andouter beam regions 816 b are provided below in the discussion of FIG.8B.

FIG. 8B shows a cross-sectional view along axis A-A of the first TGAF802 shown in FIG. 8A. The cross-sectional view shows a substrate 860over which a first sacrificial layer 861 is deposited. The substrate 860and the first sacrificial layer 861 can be similar to the substrate 726and the first sacrificial layer 701 discussed above in relation to FIGS.7A and 7B. FIG. 8B also shows cross-sections of the projections 806 a ofthe first mold mesa 806, the U-shaped beam regions 816 a, and the outerbeam regions 816 b of the second portion 816 of the looped drive beam807. As mentioned above, the U-shaped beam regions 816 a are formed onthe sidewalls of the projections 806 a within the narrow channelsbetween the projections 806 a while the outer beam regions 816 b areformed on the outside of the outermost projections 806 a, as shown inFIG. 8A.

Gaps d_(u) between opposing walls of adjacent projections 806 a arerelatively narrow, resulting in deep, narrow channels between theprojections 806 a. With such geometry, when the beam material isdeposited on the sidewalls of the projections 806 a, fewer depositionions of the deposition material reach and coat the sidewalls of theprojections 806 a within these deep narrow channels. As result, thethickness t₁ of the U-shaped beam regions 816 a within these channels isless than the thickness t₂ of the outer beam regions 816 b formedoutside of the channels and over the remainder of second portion 816 ofthe looped drive beam 807.

The thinner U-shaped beam regions 816 a, because of their geometry andvariations in thickness develop a certain amount of stress or a stressgradient. When the shutter assembly 800 is released, that is, when thesacrificial mold 804 is removed, this stress or stress gradient causesthe generally U-shaped beam regions 816 a to widen. FIG. 8C shows theshutter assembly 800 after being released from the sacrificial mold 804.The stress in the first TGAF 802 causes the first TGAF 802 to widen. Asa result of this widening, the looped drive beam 807 bends closertowards the load beam 809 resulting in a reduction in the tip-gap toTG2. For comparison, the original position of the looped drive beam 807prior to release is shown in broken lines.

In some implementations, the reduction in the tip-gap is about 0.1 to 2microns, or about 50% of the tip-gap without a TGAF. The reduction inthe tip-gap results in a reduction in the actuation voltage needed bythe actuator 826 for operating the shutter assembly 800. For example,the reduction of tip gap from 3 microns to 2 microns could result in areduction in the actuation voltage from about 25V to about 15V (or areduction of up to about 50%)

In some implementations, the channel width (indicated in FIG. 8B byd_(c)) between the U-shaped beam regions 816 a of the first TGAF 802 canbe around 3 to 6 microns. As photolithography processes improve, thesethe channel widths may reduce further. In some implementations, a lengthof the U-shaped beam regions 816 a within a plane that is parallel tothe substrate, and indicated by L in FIG. 8A, can be around 4 to 8microns.

In some implementations, the U-shaped beam regions 816 a of the firstTGAF 802 may not be adjacent to each other as shown in FIG. 8A. Instead,the U-shaped beam regions 816 a may be distributed over the length ofthe second portion 816 of the looped drive beam 807. In someimplementations, this can be achieved by forming narrow channels intothe body of the first mold mesa 806 instead of between projectionsextending out from the first mold mesa 806. The beam material depositedon the sidewalls of the first mold mesa 806 within these narrow channelsform U-shaped beam regions that are thinner than the remainder of thesecond portion 816 of the looped drive beam 807. In suchimplementations, the combined action of the distributed U-shaped beamregions can cause the looped drive beam 807 to bend towards the loadbeam 809. In such implementations, the thicknesses of the second portion816 along the U-shaped beam regions would be less than the thickness ofthe remainder of the second portion 816 of the looped drive beam 807.

FIG. 8D shows a top view of another example shutter assembly 850including the first TGAF 802. The shutter assembly 850 includes agenerally U-shaped segment 828 within the first portion 814 of thelooped drive beam 807 in addition to the first TGAF 802 incorporatedinto the second portion 816 of the looped drive beam 807. In someimplementations, the U-shaped segment 828 can have relatively smallerdimensions than that of a single U-shaped beam region 816 a of the firstTGAF 802. As discussed above, the widening of the first TGAF 802 causesthe looped drive beam 807 to bend towards the load beam 809. The bendingof the looped drive beam 807 also causes the first portion 814 to bendtowards the load beam 809. The U-shaped segment 828 allows the firstportion 814 to more easily bend at the U-shaped segment 828. As such,the U-shaped segment 828 can act as a hinge along which the firstportion 814 can bend. Thus, by allowing the first portion 814 to bendmore readily, the U-shaped segment 828 reduces the stiffness of thefirst portion 814. This reduced stiffness in the first portion 814 canallow the looped drive beam 807 to bend even further towards the loadbeam 809, thus, further reducing the tip gap TG2. In someimplementations, the first portion 814 may include more than oneU-shaped segment 828.

FIGS. 9A-9H show various views of an example shutter assembly 900 havinga second tip-gap adjustment feature (TGAF) 902. In particular, FIG. 9Ashows a top view of the shutter assembly 900, FIGS. 9B-9G showcross-sectional views of a mold 904 and the shutter assembly 900, andFIG. 9H shows a top view of the shutter assembly 900 after release,illustrating a reduction in tip-gap due to the TGAF 902.

Similar to FIG. 8A, FIG. 9A shows the shutter assembly 900 at a stage ofmanufacture that precedes the release of the shutter assembly 900 from asacrificial mold 904. The shutter assembly 900 includes an actuator 926,which includes a looped drive beam 907 and a load beam 909. The loopeddrive beam 907 is coupled to a drive anchor 920 and surrounds a firstmold mesa 906. The looped drive beam 907 includes a first portion 914, asecond portion 916 and a connecting portion 918. The load beam 909 hasone end coupled to a load anchor 922 and the other end coupled to ashutter 910. The looped drive beam 907 and the load beam 909 have atip-gap denoted by TG3.

The mold 904 also includes a second mold mesa 908 having sidewalls overwhich the load beam 909, a spring beam 912 and a peripheral beam 913 areformed. The spring beam 912 has one end coupled to the shutter 910 andthe other end coupled to the spring anchor 924. The shutter 910 isformed on the top surface of the second mold mesa 908. The peripheralbeam 913 has one end coupled to the load anchor 922 and the other endcoupled to the spring anchor 924. Similar to the shutter assembly 800shown in FIG. 8A, the shutter assembly 900 entirely surrounds the moldmesas over which the shutter assembly 900 is built. For example, thelooped drive beam 907 entirely surrounds the first mold mesa 906, andthe combination of the load beam 909, the spring beam 912, and theperipheral beam 913 entirely surround the second mold mesa 908, reducingthe number of photolithography steps needed to build the shutterassembly 900.

The looped drive beam 907 includes a second TGAF. In particular, thesecond portion 916 of the looped drive beam 907 includes ashallow-angled segment 902 between the second portion 916 and the driveanchor 920. The shallow-angled segment 902 partially surrounds a portion906 a (hereinafter referred to as “the proximal mesa portion 906 a”) ofthe first mold mesa 906 that is proximal to the anchor 920. Theshallow-angled segment 902 is configured to be thinner than at least apart of the second portion 916. This variation in thickness between theshallow-angled segment 902 and the remainder of the second portion 916results in a stress or stress gradient within the looped drive beam 907such that, after release, the tip of the looped drive beam 907 bendstowards the load beam 909, reducing the tip-gap TG3.

In some implementations, the thinner shallow-angled segment 902 is aresult of disproportionate etching of the beam material forming theshallow-angled segment 902 in comparison to the etching of the beammaterial forming the remainder of the second portion 916 of the loopeddrive beam 907. The shallow-angled segment 902 is formed on thesidewalls of the proximal mesa portion 906 a. This proximal mesa portion906 a is relatively larger in area than a distal mesa portion 906 b ofthe first mold mesa 906. In some implementations, some portions of themold mesa contract during the process of curing the mold, prior to thedeposition of the beam material. The extent to which a portion contractsis a function, in part, of the area of the portion. For example,portions with larger area may contract more than portions withrelatively smaller area. Thus, during the curing process of the firstmold mesa 906, the proximal mesa portion 906 a, which has a larger areathan the distal mesa portion 906 b, contracts more than the distal mesaportion 906 b. Furthermore, because the first mold mesa 906 is coupledto an underlying mold layer (a first sacrificial layer 961 shown inFIGS. 9B-9D), the ability of the mold material at the bottom of thefirst mold mesa 906 to contract is constrained. Thus, the proximal mesaportion 906 a contracts more at its top surface than at its bottomsurface. This results in sidewalls of the proximal mesa portion 906 ahaving a shallower angle with respect to the substrate than thesidewalls of the distal mesa portion 906 b.

FIGS. 9B-9G show cross sectional views of the first mold mesa 906 alongthe axis B-B and C-C (shown in FIG. 9A). In particular, FIGS. 9B, 9D and9F show cross sectional views of the proximal mesa portion 906 a andFIGS. 9C, 9E and 9G show cross sectional views of the distal mesaportion 906 b. FIGS. 9B and 9C show cross-sectional views of theproximal mesa portion 906 a and the distal mesa portion 906 b,respectively, after the mold 904 has been patterned and cured. The firstmold mesa 906, including the distal mesa portion 906 b and the proximalmesa portion 906 a are formed over a first sacrificial layer 961 and asubstrate 960. The first sacrificial layer 961 can be similar to thefirst sacrificial layer 861 discussed above in relation to shutterassembly 800 of FIG. 8B. As discussed above, the proximal mesa portion906 a forms a shallower angle with respect to the substrate than thedistal mesa portion 906 b. This is shown in FIGS. 9B and 9C, where thesidewalls of the proximal mesa portion 906 a form a shallower angle withrespect to the substrate as compared to the angle formed by thesidewalls of the distal mesa portion 906 b. Subsequently, as shown inFIGS. 9D and 9E, a beam material 950 is deposited over the entire firstmold mesa 906 using methods such as CVD, or PECVD. As a result, the beammaterial 950 is deposited over the sidewalls of both the proximal mesaportion 906 a and the distal mesa portion 906 b. After the deposition ofthe beam material 950, the beam material 950 is patterned to form thelooped drive beam 907. Typically, an anisotropic etching process is usedto pattern the beam material 950. Example anisotropic etching processesare discussed above in relation to FIG. 7C. The anisotropic etchingprocess etches the beam material 950 in a direction that issubstantially normal to the substrate. As the beam material 950 alongthe sidewall of the proximal mesa portion 906 a is at a shallower anglewith respect to the substrate (as shown in FIG. 9D) than that of thebeam material 950 along the sidewall of the distal mesa portion 906 b(as shown in FIG. 9E), the beam material along the proximal mesa portion906 a would be etched to a larger extent. As a result, as shown in FIGS.9F and 9G, the thicknesses of the shallow-angled segment 902 and thefirst portion 914 formed on the proximal mesa portion 906 a are lessthan the thicknesses of the first portion 914 and the second portion 916formed over the distal mesa portion 906 b.

FIG. 9H shows the shutter assembly 900 after being released from themold 904. In particular, FIG. 9H shows how the shallow-angled segment902 of the looped drive beam 907 causes the looped drive beam 907 tobend closer to the load beam 909. This results in a tip-gap of TG4,which is less than the tip-gap TG3 shown in FIG. 9A. This reduction inthe tip-gap provides a reduction in the actuation voltage needed toactuate the actuator 926.

In some implementations, the proximal mesa portion 906 a can have curvedor rounded corners as opposed to the relatively square corners shown inFIG. 9A. This will result in a curved or rounded shallow-angle segmentin the second portion 916 of the looped drive beam 907.

In some implementations, the shutter assembly 900 can also include agenerally U-shaped segment on the first portion 914 of the looped drivebeam 907 similar to the U-shaped segment 828 on the first portion 814 ofthe looped drive beam 807 of the shutter assembly 800 shown in FIG. 8D.The U-shaped segment on the first portion 914 can reduce the stiffnessof the first portion 914 and allow the looped drive beam 907 to bendeven further towards the load beam 909, and reduce the tip-gap evenfurther.

In some implementations, the spring beam 912 of the shutter assembly 900may be replaced by a second actuator, opposing the actuator 926. In suchimplementations, shutter 910 can be operated to move between open andclosed positions based on the combined action of the actuator 926 andthe opposing second actuator. The second actuator can also include alooped drive beam and a load beam attached to the shutter 910. Thelooped drive beam of the second actuator can be formed on a mold mesasimilar to the first mold mesa 906 over which the looped drive beam 907is formed. Furthermore, the looped drive beam of the second actuator mayalso include a TGAF similar to the second TGAF 902 shown in FIG. 9A.

FIGS. 10A-10C show various views of an example shutter assembly 1000having a third tip-gap adjustment feature (TGAF) 1002. In particular,FIG. 10A shows a top view of the shutter assembly 1000, FIG. 10B showsan isometric view of the third TGAF 1002, and FIG. 10C shows a top viewof the shutter assembly 1000 after release, indicating a reduction inthe tip-gap as a result of the third TGAF 1002.

The shutter assembly 1000 of FIG. 10A is similar to the shutterassemblies 800 and 900 shown in FIGS. 8A and 9A in that the shutterassembly 1000 is also formed using a sidewall beam process using a mold,such as the mold 1004. FIG. 10A shows the shutter assembly 1000 at astage of manufacture that precedes the release of the shutter assembly1000. That is, FIG. 10A shows a stage after the shutter or beam materialhas been patterned over the mold 1004. The shutter assembly 1000includes an actuator 1026, which in turn includes a looped drive beam1007 and a load beam 1009. The looped drive beam 1007 is coupled to adrive anchor 1020 and surrounds a first mold mesa 1006. The looped drivebeam 1007 includes a first portion 1014, a second portion 1016 and aconnecting portion 1018. The load beam 1009 has one end coupled to aload anchor 1022 and the other end coupled to a shutter 1010. The loopeddrive beam 1007 and the load beam 1009 have a tip-gap denoted by TG5.

The mold 1004 also includes a second mold mesa 1008 having sidewallsover which the load beam 1009, a spring beam 1012 and a peripheral beam1013 are formed. The spring beam 1012 has one end coupled to the shutter1010 and the other end coupled to the spring anchor 1024. The shutter1010 is formed on the top surface of the second mold mesa 1008. Theperipheral beam 1013 has one end coupled to the load anchor 1022 and theother end coupled to the spring anchor 1024. The peripheral beam 1013serves the same purpose as the peripheral beams 813 and 913 shown inFIGS. 8A and 9A, respectively. In particular, the incorporation of theperipheral beam 1013 allows the shutter assembly to entirely enclose thesecond mold mesa 1008, thereby avoiding any need for separation ofactuator components by using additional costly photolithographyprocesses.

The looped drive beam 1007 includes the third TGAF 1002. In particular,the second portion 1016 of the looped drive beam 1007 includes a shelfstructure 1002. The shelf structure includes a first shelf element 1002a and a second shelf element 1002 b. As discussed below, the shelfelements 1002 a and 1002 b may have some amount of stress or stressgradient. In some implementations, the stress can be in the range ofabout +/−100 MPa to about +/−200 MPa. In some implementations, thestress gradient can be about +/−400 MPa/micron. This stress or stressgradient contributes to a bending of the looped drive beam 1007 towardsthe load beam 1008. This bending causes the tip-gap between the loopeddrive beam 1007 and the load beam 1008 to decrease, which in turnresults in a decrease in the actuation voltage needed to operate theshutter assembly 1000.

FIG. 10B shows an isometric view of the shelf structure 1002. The secondsection 1016 of the looped derive beam 1007 is formed on a sidewall ofthe first mold section 1006. Both the first shelf element 1002 a and thesecond shelf element 1002 b are substantially flat structures that aresubstantially horizontal or parallel to the substrate on which theshutter assembly 1000 is built. The first shelf element 1002 a islocated at the base of the vertical surface of the second section 1016,while the second shelf element 1002 b is located at the top of thevertical surface of the second section 1016. The shelf structure 1002can be formed during patterning of the shutter and beam materialdeposited over the mold 904.

In some manufacturing processes, material that is deposited on a surfacethat is substantially parallel to an underlying substrate may developmechanical stress or a stress gradient within the plane of the surface.Thus, the first and second shelf elements 1002 a and 1002 b, which aresubstantially parallel to the substrate on which the shutter assembly1002 is built, can develop a stress or a stress gradient during theirdeposition. This stress or stress gradient may cause, upon release ofthe shutter assembly 1000, an expansion of the shelf elements 1002 a and1002 b in a direction that is parallel to the substrate. This expansionof the shelf elements 1002 a and 1002 b may cause bending in the loopeddrive beam 1007, forcing the tip 1018 closer to the load beam 1009.

FIG. 10C shows a top view of the shutter assembly 1000 of FIG. 10A afterthe shutter assembly has been released. That is, the mold 1004 includingthe first mold mesa 1006 and the second mold mesa 1008 is removed. Afterthe shutter assembly 1000 is released, the stress or stress gradients inthe shelf structure 1002 can bend the looped drive beam 1007 towards theload beam 1009. Due to the bending of the looped drive beam 1007, thetip-gap is reduced, as indicated by TG6. As seen in FIG. 10C, TG6 isless than TG5—the tip-gap that a looped drive beam would have withoutany tip-gap adjustment.

In some implementations, the second portion 1016 of the looped drivebeam 1007 can include only one, instead of two, shelf elements. In someother implementations, the second portion 1016 of the looped drive beam1007 can include more than two shelf elements. In some implementations,the second portion 1016 of the looped drive beam 1007 can include morethan one shelf structures 1002, each having one or more shelf elements.

In some implementations, the shutter assembly 1000 can also include agenerally U-shaped segment on the first portion 1014 of the looped drivebeam 1007 similar to the U-shaped segment 828 on the first portion 814of the looped drive beam 807 of the shutter assembly 800 shown in FIG.8D. The U-shaped segment on the first portion 1014 can reduce thestiffness of the first portion 1014 and allow the looped drive beam 1007to bend even further towards the load beam 1009, and reduce the tip-gapTG6 even further.

In some implementations, the spring beam 1012 of the shutter assembly1000 may be replaced by a second actuator, opposing the actuator 1026.In such implementations, shutter 1010 can be operated to move between anopen and closed position based on the combined action of the actuator1026 and the opposing second actuator. The second actuator can alsoinclude a looped drive beam and a load beam attached to the shutter1010. The looped drive beam of the second actuator can be formed on amold mesa similar to the first mold mesa 1006 over which the loopeddrive beam 1007 is formed. Furthermore, the looped drive beam of thesecond actuator may also include a TGAF similar to the third TGAF 1002shown in FIG. 10A.

In some implementations, a drive beam of a shutter assembly may includea combination of two or more of the first TGAF 802 (as shown in FIG.8A), the second TGAF 902 (as shown in FIG. 9A), the third TGAF 1002 (asshown in FIG. 10A) and the U-shaped segment 828 (as shown in FIG. 8D).

FIG. 11 shows a flow diagram of an example process 1100 for forming ashutter assembly with tip-gap adjustment feature. In particular, theprocess 1100 includes forming a mold over a substrate (stage 1102),forming a light modulator over a surface of the mold (stage 1104),forming a load beam coupled to the light modulator on a first sidewallof the mold (stage 1106), forming a first portion of a looped drive beamon a second sidewall of the mold facing the first sidewall (stage 1108),and forming a second portion of the drive beam on a third sidewallfacing away from the first sidewall such that a thickness of the secondportion varies along a length of the second portion (stage 1110).

The process 1100 begins with forming a mold on a substrate (stage 1102).Forming a mold on the substrate includes depositing and patterning asacrificial material over the substrate. One example of this processstage (stage 1102) is discussed above with respect to FIGS. 8A and 8B,in which layers of sacrificial material are deposited over a substrate860. The layers of sacrificial material are then patterned to form thefirst mold mesa 806 and the second mold mesa 808. Another example ofthis process stage (stage 1102) is discussed above in relation to FIGS.9A and 9B, in which layers of sacrificial layers are deposited over asubstrate 960. The layers of sacrificial material are then patterned toform the first mold mesa 906 and the second mold mesa 908.

The process 1100 also includes forming a light modulator over the mold(stage 1104). An example of a light modulator formed over a mold isshown in FIG. 8A, in which the shutter 810 is formed over the topsurface of the second mold mesa 808. The process 1100 also includesforming a load beam coupled to the light modulator on a first sidewallof the mold (stage 1106). This, for example, is also shown in FIG. 8A,discussed above. More particularly, FIG. 8A shows the load beam 809formed on a sidewall of the second mold mesa 808. The load beam is alsocoupled to the shutter 810. Another example, of the light modulatorformed over the mold and of a load beam formed on a first sidewall(stages 1104 and 1106) is discussed above in relation to FIG. 9A. Asshown in FIG. 9A, the shutter 910 and the load beam 909 are formed overthe top surface and the sidewalls, respectively, of the second mold mesa908. FIG. 9A also shows that the load beam 909 is coupled to the shutter910.

Furthermore, the process 1100 includes forming a first portion of adrive beam on a second sidewall of the mold facing the first sidewall(stage 1108). Examples of this process stage (stage 1108) are shown inFIGS. 8A and 9A. In FIG. 8A, the first portion 814 of the looped drivebeam 807 is formed on a sidewall of the first mold mesa 806. Thesidewall on which the first portion 814 is formed faces the sidewall onwhich the load beam 809 is formed. Similarly, FIG. 9A shows the firstportion 914 of the looped drive beam 907 formed on a sidewall of thefirst mold mesa 906 that faces the sidewall on which the load beam 909is formed.

Finally, the process 1100 includes forming a second portion of the drivebeam on a third sidewall facing away from the first sidewall such that athickness of the second portion varies along a length of the secondportion (stage 1110). An example of this processing stage (stage 1110)is shown in FIG. 8A. More particularly, FIG. 8A shows the second portion816 of the looped drive beam 807 formed on a sidewall of the first moldmesa 806 that faces away from the sidewall on the second mold mesa 808on which the load beam 809 is formed. Furthermore, the second portion816 of the looped drive beam 807 includes a first TGAF 802, in which thethickness of the looped drive beam 807 is less than the thickness of theremainder of the second portion 816 of the looped drive beam 807. Asdiscussed above in relation to FIG. 8A, the TGAF 802 includes U-shapedbeam regions 816 a formed over sidewalls of a number of projections 806a extending out from the first mold mesa 806, having narrow channelsbetween them. The U-shaped beam regions 816 a formed within these narrowchannels are thinner than the remainder of the second portion 816 of thelooped drive beam 807, as shown in FIG. 8B. Another example of thisprocessing stage (stage 1110) is shown in FIG. 9A, in which the secondportion 916 of the looped drive beam 907 is formed on a sidewall of thefirst mold mesa 906 that faces away from the sidewall on the second moldmesa 908 on which the load beam 909 is formed. Furthermore, the secondportion 916 of the looped drive beam 907 includes the shallow-angledsegment 902, which is thinner than the remainder of the second portion916. As discussed above in relation to FIG. 9A, the shallow-angledsegment 902 is formed over the proximal mesa portion 906 a of the firstmold mesa 906. When the sidewalls of the proximal mesa portion 906 a arecured, before the deposition of the beam material, these sidewalls canform a shallower angle with respect to the substrate than the sidewallsof the distal mesa portion 906 b, as shown in FIGS. 9B and 9C.Anisotropically etching beam material deposited on these shallowerangled sidewalls results in a thinner shallow-angled segment 902, asshown in FIG. 9F.

FIGS. 12A and 12B are system block diagrams illustrating a displaydevice 40 that includes a set of display elements. The display device 40can be, for example, a smart phone, a cellular or mobile telephone.However, the same components of the display device 40 or slightvariations thereof are also illustrative of various types of displaydevices such as televisions, computers, tablets, e-readers, hand-helddevices and portable media devices.

The display device 40 includes a housing 41, a display 30, an antenna43, a speaker 45, an input device 48 and a microphone 46. The housing 41can be formed from any of a variety of manufacturing processes,including injection molding, and vacuum forming. In addition, thehousing 41 may be made from any of a variety of materials, including,but not limited to: plastic, metal, glass, rubber and ceramic, or acombination thereof. The housing 41 can include removable portions (notshown) that may be interchanged with other removable portions ofdifferent color, or containing different logos, pictures, or symbols.

The display 30 may be any of a variety of displays, including abi-stable or analog display, as described herein. The display 30 alsocan be configured to include a flat-panel display, such as plasma,electroluminescent (EL) displays, OLED, super twisted nematic (STN)display, LCD, or thin-film transistor (TFT) LCD, or a non-flat-paneldisplay, such as a cathode ray tube (CRT) or other tube device. Inaddition, the display 30 can include a mechanical light modulator-baseddisplay, as described herein.

The components of the display device 40 are schematically illustrated inFIG. 12A. The display device 40 includes a housing 41 and can includeadditional components at least partially enclosed therein. For example,the display device 40 includes a network interface 27 that includes anantenna 43 which can be coupled to a transceiver 47. The networkinterface 27 may be a source for image data that could be displayed onthe display device 40. Accordingly, the network interface 27 is oneexample of an image source module, but the processor 21 and the inputdevice 48 also may serve as an image source module. The transceiver 47is connected to a processor 21, which is connected to conditioninghardware 52. The conditioning hardware 52 may be configured to conditiona signal (such as filter or otherwise manipulate a signal). Theconditioning hardware 52 can be connected to a speaker 45 and amicrophone 46. The processor 21 also can be connected to an input device48 and a driver controller 29. The driver controller 29 can be coupledto a frame buffer 28, and to an array driver 22, which in turn can becoupled to a display array 30. One or more elements in the displaydevice 40, including elements not specifically depicted in FIG. 12A, canbe configured to function as a memory device and be configured tocommunicate with the processor 21. In some implementations, a powersupply 50 can provide power to substantially all components in theparticular display device 40 design.

The network interface 27 includes the antenna 43 and the transceiver 47so that the display device 40 can communicate with one or more devicesover a network. The network interface 27 also may have some processingcapabilities to relieve, for example, data processing requirements ofthe processor 21. The antenna 43 can transmit and receive signals. Insome implementations, the antenna 43 transmits and receives RF signalsaccording to the IEEE 16.11 standard, including IEEE 16.11(a), (b), or(g), or the IEEE 802.11 standard, including IEEE 802.11a, b, g, n, andfurther implementations thereof. In some other implementations, theantenna 43 transmits and receives RF signals according to the Bluetooth®standard. In the case of a cellular telephone, the antenna 43 can bedesigned to receive code division multiple access (CDMA), frequencydivision multiple access (FDMA), time division multiple access (TDMA),Global System for Mobile communications (GSM), GSM/General Packet RadioService (GPRS), Enhanced Data GSM Environment (EDGE), TerrestrialTrunked Radio (TETRA), Wideband-CDMA (W-CDMA), Evolution Data Optimized(EV-DO), 1xEV-DO, EV-DO Rev A, EV-DO Rev B, High Speed Packet Access(HSPA), High Speed Downlink Packet Access (HSDPA), High Speed UplinkPacket Access (HSUPA), Evolved High Speed Packet Access (HSPA+), LongTerm Evolution (LTE), AMPS, or other known signals that are used tocommunicate within a wireless network, such as a system utilizing 3G, 4Gor 5G technology. The transceiver 47 can pre-process the signalsreceived from the antenna 43 so that they may be received by and furthermanipulated by the processor 21. The transceiver 47 also can processsignals received from the processor 21 so that they may be transmittedfrom the display device 40 via the antenna 43.

In some implementations, the transceiver 47 can be replaced by areceiver. In addition, in some implementations, the network interface 27can be replaced by an image source, which can store or generate imagedata to be sent to the processor 21. The processor 21 can control theoverall operation of the display device 40. The processor 21 receivesdata, such as compressed image data from the network interface 27 or animage source, and processes the data into raw image data or into aformat that can be readily processed into raw image data. The processor21 can send the processed data to the driver controller 29 or to theframe buffer 28 for storage. Raw data typically refers to theinformation that identifies the image characteristics at each locationwithin an image. For example, such image characteristics can includecolor, saturation and gray-scale level.

The processor 21 can include a microcontroller, CPU, or logic unit tocontrol operation of the display device 40. The conditioning hardware 52may include amplifiers and filters for transmitting signals to thespeaker 45, and for receiving signals from the microphone 46. Theconditioning hardware 52 may be discrete components within the displaydevice 40, or may be incorporated within the processor 21 or othercomponents.

The driver controller 29 can take the raw image data generated by theprocessor 21 either directly from the processor 21 or from the framebuffer 28 and can re-format the raw image data appropriately for highspeed transmission to the array driver 22. In some implementations, thedriver controller 29 can re-format the raw image data into a data flowhaving a raster-like format, such that it has a time order suitable forscanning across the display array 30. Then the driver controller 29sends the formatted information to the array driver 22. Although adriver controller 29, such as an LCD controller, is often associatedwith the system processor 21 as a stand-alone Integrated Circuit (IC),such controllers may be implemented in many ways. For example,controllers may be embedded in the processor 21 as hardware, embedded inthe processor 21 as software, or fully integrated in hardware with thearray driver 22.

The array driver 22 can receive the formatted information from thedriver controller 29 and can re-format the video data into a parallelset of waveforms that are applied many times per second to the hundreds,and sometimes thousands (or more), of leads coming from the display'sx-y matrix of display elements.

In some implementations, the driver controller 29, the array driver 22,and the display array 30 are appropriate for any of the types ofdisplays described herein. For example, the driver controller 29 can bea conventional display controller or a bi-stable display controller.Additionally, the array driver 22 can be a conventional driver or abi-stable display driver. Moreover, the display array 30 can be aconventional display array or a bi-stable display array. In someimplementations, the driver controller 29 can be integrated with thearray driver 22. Such an implementation can be useful in highlyintegrated systems, for example, mobile phones, portable-electronicdevices, watches or small-area displays.

In some implementations, the input device 48 can be configured to allow,for example, a user to control the operation of the display device 40.The input device 48 can include a keypad, such as a QWERTY keyboard or atelephone keypad, a button, a switch, a rocker, a touch-sensitivescreen, a touch-sensitive screen integrated with the display array 30,or a pressure- or heat-sensitive membrane. The microphone 46 can beconfigured as an input device for the display device 40. In someimplementations, voice commands through the microphone 46 can be usedfor controlling operations of the display device 40.

The power supply 50 can include a variety of energy storage devices. Forexample, the power supply 50 can be a rechargeable battery, such as anickel-cadmium battery or a lithium-ion battery. In implementationsusing a rechargeable battery, the rechargeable battery may be chargeableusing power coming from, for example, a wall socket or a photovoltaicdevice or array. Alternatively, the rechargeable battery can bewirelessly chargeable. The power supply 50 also can be a renewableenergy source, a capacitor, or a solar cell, including a plastic solarcell or solar-cell paint. The power supply 50 also can be configured toreceive power from a wall outlet.

In some implementations, control programmability resides in the drivercontroller 29 which can be located in several places in the electronicdisplay system. In some other implementations, control programmabilityresides in the array driver 22. The above-described optimization may beimplemented in any number of hardware and/or software components and invarious configurations.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover: a, b, c,a-b, a-c, b-c, and a-b-c.

The various illustrative logics, logical blocks, modules, circuits andalgorithm processes described in connection with the implementationsdisclosed herein may be implemented as electronic hardware, computersoftware, or combinations of both. The interchangeability of hardwareand software has been described generally, in terms of functionality,and illustrated in the various illustrative components, blocks, modules,circuits and processes described above. Whether such functionality isimplemented in hardware or software depends upon the particularapplication and design constraints imposed on the overall system.

The hardware and data processing apparatus used to implement the variousillustrative logics, logical blocks, modules and circuits described inconnection with the aspects disclosed herein may be implemented orperformed with a general purpose single- or multi-chip processor, adigital signal processor (DSP), an application specific integratedcircuit (ASIC), a field programmable gate array (FPGA) or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, or any combination thereof designed to perform thefunctions described herein. A general purpose processor may be amicroprocessor, or, any conventional processor, controller,microcontroller, or state machine. A processor also may be implementedas a combination of computing devices, such as a combination of a DSPand a microprocessor, a plurality of microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration. In some implementations, particular processes and methodsmay be performed by circuitry that is specific to a given function.

In one or more aspects, the functions described may be implemented inhardware, digital electronic circuitry, computer software, firmware,including the structures disclosed in this specification and theirstructural equivalents thereof, or in any combination thereof.Implementations of the subject matter described in this specificationalso can be implemented as one or more computer programs, i.e., one ormore modules of computer program instructions, encoded on a computerstorage media for execution by, or to control the operation of, dataprocessing apparatus.

If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. The processes of a method or algorithmdisclosed herein may be implemented in a processor-executable softwaremodule which may reside on a computer-readable medium. Computer-readablemedia includes both computer storage media and communication mediaincluding any medium that can be enabled to transfer a computer programfrom one place to another. A storage media may be any available mediathat may be accessed by a computer. By way of example, and notlimitation, such computer-readable media may include RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that may be used to storedesired program code in the form of instructions or data structures andthat may be accessed by a computer. Also, any connection can be properlytermed a computer-readable medium. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk, and blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Combinations of the above should also be included within the scope ofcomputer-readable media. Additionally, the operations of a method oralgorithm may reside as one or any combination or set of codes andinstructions on a machine readable medium and computer-readable medium,which may be incorporated into a computer program product.

Various modifications to the implementations described in thisdisclosure may be readily apparent to those skilled in the art, and thegeneric principles defined herein may be applied to otherimplementations without departing from the spirit or scope of thisdisclosure. Thus, the claims are not intended to be limited to theimplementations shown herein, but are to be accorded the widest scopeconsistent with this disclosure, the principles and the novel featuresdisclosed herein.

Additionally, a person having ordinary skill in the art will readilyappreciate, the terms “upper” and “lower” are sometimes used for ease ofdescribing the figures, and indicate relative positions corresponding tothe orientation of the figure on a properly oriented page, and may notreflect the proper orientation of any device as implemented.

Certain features that are described in this specification in the contextof separate implementations also can be implemented in combination in asingle implementation. Conversely, various features that are describedin the context of a single implementation also can be implemented inmultiple implementations separately or in any suitable subcombination.Moreover, although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Further, the drawings may schematically depict one more exampleprocesses in the form of a flow diagram. However, other operations thatare not depicted can be incorporated in the example processes that areschematically illustrated. For example, one or more additionaloperations can be performed before, after, simultaneously, or betweenany of the illustrated operations. In certain circumstances,multitasking and parallel processing may be advantageous. Moreover, theseparation of various system components in the implementations describedabove should not be understood as requiring such separation in allimplementations, and it should be understood that the described programcomponents and systems can generally be integrated together in a singlesoftware product or packaged into multiple software products.Additionally, other implementations are within the scope of thefollowing claims. In some cases, the actions recited in the claims canbe performed in a different order and still achieve desirable results.

1. A display element, comprising: a substrate; an electromechanicalsystems (EMS) electrostatic actuator coupled to the substratecomprising: a load beam electrode coupled to a light modulator; and adrive beam electrode having a first portion positioned adjacent to theload beam, a second portion positioned behind the first portion withrespect to the load beam, and an end portion connecting the firstportion to the second portion, wherein the thickness of the secondportion varies along its length.
 2. The display apparatus of claim 1,wherein the second portion of the drive beam electrode includes a firstgenerally U-shaped segment, and wherein the thickness of the drive beamelectrode along the first generally U-shaped segment is different thanthe thickness of the beam adjacent to the first generally U-shapedsegment.
 3. The display apparatus of claim 2, wherein the second portionof the drive beam electrode includes a second generally U-shaped segmentand wherein the thickness of the drive beam electrode along the firstand the second generally U-shaped segments is different than thethickness of the remainder of the second portion.
 4. The displayapparatus of claim 3, wherein the first U-shaped segment is adjacent tothe second U-shaped segment.
 5. The apparatus of claim 2, wherein thefirst portion of the drive beam electrode includes a third generallyU-shaped segment, smaller than the first U-shaped segment of the secondportion.
 6. The apparatus of claim 1, wherein a segment of the secondportion of the drive beam electrode has an angle with respect to thesubstrate that is shallower than an angle formed by a remainder of thesecond portion of the drive beam electrode with respect to thesubstrate.
 7. The apparatus of claim 6, wherein the segment of thesecond portion of the drive beam electrode having the shallower anglewith respect to the substrate is thinner than the remainder of thesecond portion of the substrate.
 8. The apparatus of claim 1, whereinthe first portion, the end portion, and the second portion of the drivebeam form a loop.
 9. The apparatus of claim 1, further comprising: adisplay; a processor that is configured to communicate with the display,the processor being configured to process image data; and a memorydevice that is configured to communicate with the processor.
 10. Theapparatus of claim 9, further comprising: a driver circuit configured tosend at least one signal to the display; and a controller configured tosend at least a portion of the image data to the driver circuit.
 11. Theapparatus of claim 9, further comprising: an image source moduleconfigured to send the image data to the processor, wherein the imagesource module comprises at least one of a receiver, transceiver, andtransmitter.
 12. The apparatus of claim 9, further comprising: an inputdevice configured to receive input data and to communicate the inputdata to the processor.
 13. A display element, comprising: a substrate;an electromechanical systems (EMS) electrostatic actuator coupled to thesubstrate comprising: a load beam electrode coupled to a lightmodulator; and a drive beam electrode coupled to the substrate having: afirst portion positioned adjacent to the load beam electrode, a secondportion positioned behind the first portion with respect to the loadbeam electrode, an end portion connecting the first portion to thesecond portion, and a shelf structure separate from an anchor supportingthe drive beam over the substrate, having a first planar surface that issubstantially parallel to the substrate and coupled to the secondportion of the drive beam.
 14. The display element of claim 13, whereinthe first planar surface is positioned on a side of the second portionof the drive beam that is substantially normal to the substrate.
 15. Thedisplay element of claim 13, wherein the first planar surface inpositioned on an edge of the second portion of the drive beam that facesaway from the substrate.
 16. The display element of claim 13, whereinthe shelf structure includes a second planar surface that issubstantially parallel to the substrate and coupled to the secondportion of the drive beam.
 17. The display element of claim 16, whereinthe first planar surface and the second planar surface are positioned onopposite ends of a side of the second portion that is substantiallynormal in relation to the substrate.
 18. The display element of claim13, wherein the shelf structure is physically separated from the firstportion of the drive beam.
 19. The display element of claim 13, whereinthe first portion, the end portion, and the second portion of the drivebeam form a loop.
 20. A method, comprising: forming a mold over asubstrate; forming a light modulator over a surface of the mold; forminga load beam coupled to the light modulator on a first sidewall of themold; forming a first portion of a drive beam on a second sidewall ofthe mold facing the first sidewall; and forming a second portion of thedrive beam on a third sidewall facing away from the first sidewall, suchthat a thickness of the second portion varies along a length of thesecond portion.
 21. The method of claim 20, wherein the third sidewallincludes a U-shaped portion, and wherein forming the second portionfurther includes forming a generally U-shaped segment in the secondportion along the U-shaped portion of the third sidewall such that athickness of the second portion along the U-shaped segment is differentfrom a thickness of the second portion adjacent to the generallyU-shaped segment.
 22. The method of claim 20, wherein forming the moldfurther includes forming a portion of the third sidewall at an anglewith respect to the substrate, the angle being shallower than thatformed by the second sidewall.
 23. The method of claim 22, wherein asegment of the second portion formed over the portion of the thirdsidewall having the shallower angle is thinner than the remainder of thesecond portion.